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Types of Chemical Bonds

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Chemistry

Some people work best on their own. They get on with the task with minimal input from others. But other people work best in a group. They achieve their best outcomes when they combine forces; sharing ideas, knowledge, and tasks. Neither way is better than the other - it simply depends on which method suits you the best.

Chemical bonding is very similar to this. Some atoms are much happier by themselves, while some prefer to join up with others. They do this by forming chemical bonds.

Chemical bonding is the attraction between different atoms that enables the formation of molecules or compounds. It occurs thanks to the sharing, transfer, or delocalization of electrons.

  • This article is an introduction to the types of bonding in chemistry.
  • We will look at why atoms bond.
  • We'll explore the three types of chemical bonds.
  • We'll then look at factors affecting the strength of bonding.

Why Do Atoms Bond?

At the start of this article, we introduced you to a chemical bond: the attraction between different atoms that enables the formation of molecules or compounds. But why do atoms bond to each other in this way?

Simply put, atoms form bonds in order to become more stable. For the majority of atoms, this means obtaining a full outer shell of electrons. An atom's outer shell of electrons is known as its valence shell; these valence shells typically require eight electrons to fill them up completely. This gives them the electron configuration of the noble gas closest to them in the periodic table. Achieving a full valence shell puts the atom in a lower, more stable energy state, which is known as the octet rule.

The octet rule states that the majority of atoms tend to gain, lose, or share electrons until they have eight electrons in their valence shell. This gives them the configuration of a noble gas.

But to get to this more stable energy state, atoms might need to move some of their electrons around. Some atoms have too many electrons. They find it easiest to get a full valence shell by getting rid of surplus electrons, either by donating them to another species, or by delocalizing them. Other atoms don't have quite enough electrons. They find it easiest to gain extra electrons, either by sharing them or accepting them from another species.

When we say 'easiest', we really mean 'most energetically favorable'. Atoms don't have preferences - they're simply subject to the laws of energy that govern the whole universe.

You should also note that there are some exceptions to the octet rule. For example, the noble gas helium has just two electrons in its outer shell and is perfectly stable. Helium is the noble gas nearest to a handful of elements such as hydrogen and lithium. This means that these elements are also more stable when they have just two outer shell electrons, not the eight that the octet rule predicts. Check out The Octet Rule for more information.

Moving electrons around creates differences in charges, and differences in charges cause attraction or repulsion between atoms. For example, if one atom loses an electron, it forms a positively charged ion. If another atom gains this electron, it forms a negatively charged ion. The two oppositely charged ions will be attracted to each other, forming a bond. But this is just one of the ways of forming a chemical bond. In fact, there are a few different types of bonds that you need to know about.

Types of Chemical Bonds

There are three different types of chemical bonds in chemistry.

  • Covalent bond
  • Ionic bond
  • Metallic bond

These are all formed between different species and have different characteristics. We'll start by exploring the covalent bond.

Covalent Bonds

For some atoms, the simplest way to achieve a filled-up outer shell is by gaining extra electrons. This is typically the case with non-metals, which contain a large number of electrons in their outer shell. But where can they get extra electrons from? Electrons don't just appear out of nowhere! Non-metals get around this in an innovative way: they share their valence electrons with another atom. This is a covalent bond.

A covalent bond is a shared pair of valence electrons.

A more accurate description of covalent bonding involves atomic orbitals. Covalent bonds form when valence electron orbitals overlap, forming a shared pair of electrons. The atoms are held together by electrostatic attraction between the negative electron pair and the atoms' positive nuclei, and the shared pair of electrons counts towards the valence shell of both bonded atoms. This enables them both to effectively gain an extra electron, bringing them closer to a full outer shell.

Types of chemical bonds, Covalent boning in fluorine, StudySmarter.Covalent bonding in fluorine. Anna Brewer, StudySmarter Originals

In the example above, each fluorine atom starts with seven outer shell electrons - they're one short of the eight needed to have a full outer shell. But both fluorine atoms can use one of their electrons to form a shared pair. In this way, both atoms seemingly end up with eight electrons in their outer shell.

There are three forces involved in covalent bonding.

  • The repulsion between the two positively charged nuclei.
  • The repulsion between the negatively charged electrons.
  • The attraction between the positively charged nuclei and the negatively charged electrons.

If the total strength of the attraction is stronger than the total strength of the repulsion, the two atoms will bond.

Multiple Covalent Bonds

For some atoms, such as fluorine, just one covalent bond is enough to give them that magic number of eight valence electrons. But some atoms might have to form multiple covalent bonds, sharing further pairs of electrons. They can either bond with multiple different atoms, or form a double or triple bond with the same atom.

For example, nitrogen needs to form three covalent bonds in order to achieve a full outer shell. It can either form three single covalent bonds, one single and one double covalent bond, or one triple covalent bond.

Types of Chemical Bonds, single double triple bonds, StudySmarterSingle, double, and triple covalent bonds. Anna Brewer, StudySmarter Originals

Covalent Structures

Some covalent species form discrete molecules, known as simple covalent molecules, made up of just a few atoms joined with covalent bonds. These molecules tend to have low melting and boiling points. But some covalent species form giant macromolecules, made up of an infinite number of atoms. These structures have high melting and boiling points. We saw above how a fluorine molecule is made up of just two fluorine atoms covalently bonded together. Diamond, on the other hand, contains many hundreds of atoms covalently bonded together - carbon atoms, to be precise. Each carbon atom forms four covalent bonds, creating a giant lattice structure that stretches in all directions.

Types of Chemical Bonds, diamond lattice, StudySmarterA representation of the lattice in a diamond. Image credits: commons.wikimedia.org

Check out Covalent Bonding for a more detailed explanation of covalent bonds. If you want to know more about covalent structures and the properties of covalent bonds, head over to Bonding and Elemental Properties.

Ionic Bonds

Above, we learned how non-metals effectively 'gain' extra electrons by sharing an electron pair with another atom. But bring metal and a non-metal together, and they can do one better - they actually transfer an electron from one species to the other. The metal donates its extra valence electrons, bringing it down to eight in its outer shell. This forms a positive cation. The non-metal gains these donated electrons, bringing the number of electrons up to eight in its outer shell, forming a negative ion, called an anion. In this way, both elements are satisfied. The oppositely charged ions are then attracted to each other by strong electrostatic attraction, forming an ionic bond.

An ionic bond is an electrostatic attraction between oppositely charged ions.

Types of Chemical Bonds, ionic bonding sodium chlorine chloride, StudySmarterIonic bonding between sodium and chlorine. Anna Brewer, StudySmarter Original

Here, sodium has one electron in its outer shell, whilst chlorine has seven. In order to achieve a complete valence shell, sodium needs to lose one electron whilst chlorine needs to gain one. Sodium, therefore, donates its outer shell electron to chlorine, transforming into a cation and an anion respectively. The oppositely charged ions are then attracted to each other by electrostatic attraction, holding them together.

When the loss of an electron leaves an atom with no electrons in its outer shell, we consider the shell below as the valence shell. For example, the sodium cation has no electrons in its outer shell, so we look to the one below - which has eight. Sodium, therefore, satisfies the octet rule. This is why group VIII is often called group 0; for our purposes, they mean the same thing.

Ionic Structures

Ionic structures form giant ionic lattices made up of many oppositely charged ions. They don't form discrete molecules. Each negatively charged ion is ionically bonded to all of the positively charged ions around it, and vice versa. The sheer number of ionic bonds gives ionic lattices high strength, and high melting and boiling points.

Types of Chemical Bonds ionic lattice ions StudySmarterAn ionic lattice structure. Anna Brewer, StudySmarter Originals

Covalent bonding and ionic bonding are actually closely related. They exist on a scale, with completely covalent bonds at one end and completely ionic bonds at the other. Most covalent bonds exist somewhere in the middle. We say that bonds that behave a little like ionic bonds have an ionic 'character'.

Metallic Bonds

Now we know how non-metals and metals bond with each other, and how non-metals bond with themselves or with other non-metals. But how do metals bond? They have the opposite problem to non-metals - they have too many electrons, and the easiest way for them to achieve a full outer shell is by losing their extra electrons. They do this in a special way: by delocalizing their valence shell electrons.

What happens to these electrons? They form something called a sea of delocalization. The sea surrounds the remaining metals centers, which arrange themselves into an array of positive metal ions. The ions are held in place by electrostatic attraction between themselves and the negative electrons. This is known as a metallic bond.

Metallic bonding is a type of chemical bonding found within metals. It consists of the electrostatic attraction between an array of positive metal ions and a sea of delocalized electrons.

It is important to note that the electrons aren't associated with any one metal ion in particular. Instead, they move freely between all of the ions, acting both as a glue and a cushion. This leads to good conductivity in metals.

Types of Chemical Bonds, metallic bonding sodium, StudySmarterMetallic bonding in sodium. Anna Brewer, StudySmarter Original

We learned earlier that sodium has one electron in its outer shell. When sodium atoms form metallic bonds, each sodium atom loses this outer shell electron to form a positive sodium ion with a charge of +1. The electrons form a sea of delocalization surrounding the sodium ions. The electrostatic attraction between the ions and the electrons is known as a metallic bond.

Metallic Structures

Like ionic structures, metals form giant lattices that contain an infinite number of atoms and stretch in all directions. But unlike ionic structures, they are malleable and ductile, and they usually have slightly lower melting and boiling points.

Bonding and Elemental Properties contains all you need to know about how bonding affects the properties of different structures.

Summarising Types of Bonds

We've made you a handy table to help you compare the three different types of bonding. It summarises all you need to know about covalent, ionic, and metallic bonding.

CovalentIonicMetallic
DescriptionShared pair of electronsTransfer of electronsDelocalization of electrons
Electrostatic forcesBetween the shared pair of electrons and the atoms' positive nucleiBetween oppositely charged ionsBetween positive metal ions and the sea of delocalized electrons
Structures formedSimple covalent moleculesGiant covalent macromoleculesGiant ionic latticesGiant metallic lattices
Diagram

The Strength of Chemical Bonds

If you had to guess, which type of bonding would you label as the strongest? It is actually ionic > covalent > metallic bonding. But within each type of bonding, there are certain factors that influence the bond's strength. We'll start by looking at the strength of covalent bonds.

Strength of Covalent Bonds

You'll remember that a covalent bond is a shared pair of valence electrons, thanks to the overlap of electron orbitals. There are a few factors that affect the strength of a covalent bond, and they all have to do with the size of this area of orbital overlap. These include the type of bond and the size of the atom.

  • As you move from a single covalent bond to a double or triple covalent bond, the number of overlapping orbitals increases. This increases the strength of the covalent bonding.
  • As the size of the atoms increases, the proportional size of the area of orbital overlap decreases. This decreases the strength of the covalent bonding.
  • As polarity increases, the strength of the covalent bonding increases. This is because the bond becomes more ionic in character.

Strength of Ionic Bonds

We now know that an ionic bond is an electrostatic attraction between oppositely charged ions. Any factors that affect this electrostatic attraction affect the strength of the ionic bond. These include the charge of the ions and the size of the ions.

  • Ions with a higher charge experience stronger electrostatic attraction. This increases the strength of the ionic bonding.
  • Ions with a smaller size experience stronger electrostatic attraction. This increases the strength of the ionic bonding.

Visit Ionic Bonding for a deeper exploration of this topic.

Strength of Metallic Bonds

We know that a metallic bond is an electrostatic attraction between an array of positive metal ions and a sea of delocalized electrons. Once again, any factors that affect this electrostatic attraction affect the strength of the metallic bond.

  • Metals with more delocalized electrons experience stronger electrostatic attraction, and stronger metallic bonding.
  • Metals ions with a higher charge experience stronger electrostatic attraction, and stronger metallic bonding.
  • Metal ions with a smaller size experience stronger electrostatic attraction, and stronger metallic bonding.

You can find out more at Metallic Bonding.

Bonding and Intermolecular Forces

It is important to note that bonding is completely different from intermolecular forces. Chemical bonding occurs within a compound or molecule and is very strong. Intermolecular forces occur between molecules and are much weaker. The strongest type of intermolecular force is a hydrogen bond.

Despite its name, it is not a type of chemical bond. In fact, it is ten times weaker than a covalent bond!

Go to Intermolecular Forces to find out more about hydrogen bonds and the other types of intermolecular forces.

Types of Chemical Bonds - Key takeaways

  • Chemical bonding is the attraction between different atoms that enables the formation of molecules or compounds. Atoms bond to become more stable according to the octet rule.
  • A covalent bond is a shared pair of valence electrons. It typically forms between non-metals.
  • An ionic bond is an electrostatic attraction between oppositely charged ions. It typically occurs between metals and non-metals.
  • A metallic bond is an electrostatic attraction between an array of positive metal ions and a sea of delocalized electrons. It forms within metals.
  • Ionic bonds are the strongest type of chemical bond, followed by covalent bonds and then metallic bonds. Factors affecting the strength of bonding include the size of atoms or ions, and the number of electrons involved in the interaction.

Types of Chemical Bonds

The three types of chemical bond are covalent, ionic, and metallic. 

Table salt is an example of ionic bonding. 

Chemical bonding is the attraction between different atoms that enables the formation of molecules or compounds. it occurs thanks to the sharing, transfer, or delocalization of electrons.

Ionic bonds are the strongest type of chemical bond, followed by covalent bonds, and then metallic bonds. 

Covalent bonds are found between non-metals and involve the sharing of a pair of electrons. Ionic bonds are found between non-metals and metals and involve the transfer of electrons. Metallic bonds are found between metals, and involve the delocalization of electrons. 

Final Types of Chemical Bonds Quiz

Question

Describe metallic bonding.

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Answer

The attraction between an array of positive metal ions and a sea of delocalized electrons. 

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Question

What sort of elements bond using metallic bonding?

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Answer

Just metals

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Question

True or false? Metals bond using shared pairs of electrons.

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Answer

False

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Question

Explain why magnesium experiences stronger metallic bonding than sodium.

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Answer

  • It forms ions with a higher charge and a greater proton number.
  • It has more delocalized electrons.
  • It forms smaller ions.

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Question

Explain why metals are good conductors of electricity.

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Answer

They contain delocalized electrons which are free to move and carry a charge.

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Question

Explain why metals are lustrous.

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Answer

Metals contain delocalized electrons. These absorb light energy and become excited. To return to their ground state, they release the energy as light, giving off a lustrous gleam.

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Question

True or false? Metals are brittle.

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Answer

False

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True or false? Metals have medium-high melting and boiling points.

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True

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Question

What is a covalent bond?

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Answer

A shared pair of electrons.

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Question

Which elements typically form covalent bonds?

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Answer

Non-metals

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Question

Polar covalent bonds are caused by differences in _____.

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Answer

Electronegativity

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True or false? Double covalent bonds are longer than single covalent bonds.

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Answer

False

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Question

What is a polar covalent bond?

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Answer

A bond in which the electron pair is shared unequally between the two bonded atoms.

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What causes polar covalent bonds?

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A difference in electronegativity.

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Question

True or false? The C-H bond is polar.

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Answer

False

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Question

An electronegativity difference of less than _____ results in a non-polar bond.

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Answer

0.4

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Question

An electronegativity difference between _____ and _____ results in a polar bond.

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Answer

0.4 and 1.8

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An electronegativity difference greater than _____ results in an ionic bond.

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1.8

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Predict which bond is the most polar.

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C-F

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Predict whether the C-N bond is polar, non-polar or ionic.

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Polar

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Predict whether the O-O bond is polar, non-polar or ionic.

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Non-polar

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Question

Which of the following properties indicate that a compound's bonding is covalent, not ionic?

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Answer

Low melting and boiling points

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What is an ionic bond?

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Answer

The electrostatic attraction between oppositely charged ions. 

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Ionic bonds generally form between _____.

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Answer

Metals and non-metals

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True or false? Ionic compounds form molecules.

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Answer

False

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Predict which compound has stronger ionic bonding.

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Answer

KCl

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Predict which compound has stronger ionic bonding.

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NaCl

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True or false? Ionic compounds are good conductors of electricity.

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True

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True or false? Ionic compounds are physically hard and strong.

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True

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In general, ionic compounds have ____ melting and boiling points.

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High

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Which of the following can conduct electricity?

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Metallic structures

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Ionic compounds tend to have ____ melting and boiling points compared to simple covalent molecules.

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Higher

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Which of the following are typically hard and strong?

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Answer

Ionic structures

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An unknown substance has a high melting point and is insoluble in water. Predict its structure.

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Covalent network solid 

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An unknown substance has medium-high melting and boiling points and is a good conductor of electricity when solid. Predict its structure.

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Metallic

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An unknown substance has a high solubility, high melting and boiling points and conducts electricity when aqueous. Predict its structure.

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Ionic

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An unknown substance is gaseous at room temperature. Predict its structure.

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Simple covalent molecule

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True or false? Metals are brittle.

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Answer

False

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Which substance has a higher melting point? Explain your answer.

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Answer

Giant covalent macromolecule

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What are the three types of chemical bond?

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Answer

Covalent

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What bonding would you expect to find in potassium chloride, KCl? 

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Ionic

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Covalent bonds generally form between _____.

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Non-metals

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Ionic bonds generally form between _____.

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Answer

Metals and non-metals

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Predict the type of bonding in BF3.

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Covalent

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Which type/s of bonding contain charged ions?

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Metallic only

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Which bond is stronger?

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Answer

C-O

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Which type of bonding is the weakest?

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Answer

Metallic

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Question

Some covalent bonds are polar. What determines their polarity?

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Answer

The electronegativity difference of the two atoms involved in the bond.

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True or false? An atom can only form covalent bonds with one other atom.

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Answer

False

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Question

Which type/s of bonding involve the transfer of electrons?

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Answer

Ionic only

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