Intramolecular Forces

For a molecule to be polar, two things must be true:

- The molecule must have polar bonds. - The molecule must not be symmetric, or the polar bonds will cancel each other out.

Two main types of chemical bonds can form between two atoms.

- When an electron is shared between atoms of similar electronegativity, a covalent bond is formed. - When an electron is transferred from one atom to another, an ionic bond is formed.

How many carbon (C) atoms are in the molecule CO^2?

1

How many oxygen (O) atoms are in the molecule CO^2?

2

How many single bonds can silicon (Si) form at once?

4 Silicon can form as many bonds as carbon, since they are in the same group.

What kind of bond is made up of shared electrons?

A covalent bond

Lewis Structure

A sketch of a molecule that uses dots to represent valence electrons.

Why do atoms form bonds?

Atoms tend to form bonds in order to obtain a full octet of valence electrons.

Examples of Covalent and Ionic Bonds:

Covalent: H-C B-C Li-B O-Cl F-O Ionic: Na-Br Li-F K-O Mg-F

1.7 Rule.

Tells you whether a bond will be covalent or ionic. There's an easy way to determine which bonds are covalent. It's called the 1.7 rule. This rule describes how similar the electronegativity of two elements must be in order to form a covalent bond. Using a simple subtraction problem and the periodic table, you can figure out what kinds of bonds atoms tend to create.

Intramolecular Force

The attraction that exists within a molecule.

electronegativities

The tendency of atoms in molecules to attract shared bonding electrons.

Which is the strongest bond? A single nitrogen bond A double nitrogen bond A triple nitrogen bond

The triple bond is the strongest.

What is a molecule?

Two or more atoms form a molecule when covalent bonds hold them together.

To draw a Lewis structure, follow these steps:

- Draw the electron dot diagram for each atom in the molecule. - Find the lone electrons around each atom. - Pair up one lone electron from each atom. In other words, 1 covalent bond consists of 2 lone electrons — 1 from each atom. - Replace the paired electrons with a line drawn between the 2 atoms.

What is the electronegativity difference between S and H?

0.4 Subtract 2.1 from 2.5.

How many nitrogen (N) atoms are in the molecule NH^3?

1

How many electrons does hydrogen need to gain to have a full set of valence electrons?

1 Hydrogen only needs 2 total electrons to have a full set of valence electrons.

How many electrons does chlorine need to gain to have a full octet?

1 Chlorine has 7 valence electrons, so it needs 1 more to have a full octet.

How many hydrogen (H) atoms are in the molecules NH^3?

3

In a molecule of carbon dioxide, carbon is bonded to 2 different oxygen atoms. How many total bonds is the carbon atom forming?

4 Carbon is forming 2 bonds with each oxygen atom for a total of 4 bonds.

How many dots should the Lewis structure for nitrogen have?

5 Each dot represents a valence electron, so it should have 5 dots.

How many valence electrons does nitrogen (N) have?

5 Nitrogen is in Group 15, so it has 5 valence electrons.

When you're drawing covalent bonds — single, double, or triple — there should always be a total of _______ electrons around each atom.

8

Polar Covalent Bond

A bond in which electrons are unevenly shared between atoms.

Double Bond

A covalent bond in which two electron pairs are shared between two atoms. Example: Oxygen (O) has 6 valence electrons, so if 2 oxygen atoms share 2 valence electrons each in a double bond, each atom gets a full octet. The oxygen molecule you breathe (O2) is an example of a molecule containing a double bond.

Triple Bond

A covalent bond involving the sharing of three pairs of electrons. Example: Nitrogen (N) has 5 valence electrons, so each atom needs 3 more electrons to get a full octet. The nitrogen molecule in the atmosphere (N2) is an example of a molecule with a triple bond.

Electron Dot Diagram

A diagram using dots to represent valence electrons on an atom.

Why do atoms tend to have a full set of valence electrons?

A full octet, which is 8 electrons, is very stable.

Dipole Moment

A measure of the degree of separation of charge in a polar molecule.

What kind of bond would many atoms of the same metal make?

A metallic bond

A chemical formula shows the atoms in a molecule.

A nitrogen molecule has 2 nitrogen atoms that share electrons. It is written as N2. N is the symbol on the periodic table for nitrogen. The number 2 written below the N is called a subscript.

Covalent Bond

A type of bond in which electrons are shared between atoms.

Nonpolar Covalent Bond

A type of bond in which electrons are shared equally by both atoms.

Hydrogen Bonding

A type of dipole-dipole force occurring between a hydrogen atom and a highly electronegative atom, such as nitrogen, oxygen, or fluorine. Hydrogen bonding takes place between a single hydrogen atom and a single oxygen, nitrogen, or fluorine atom.

Chemical Symbol

An abbreviation for the name of a chemical element; it consists of a single capital letter or a capital letter followed by a small letter.

Intermolecular Force

An attractive or a repulsive force between molecules.

What best classifies a bond between 2 atoms as being ionic?

An electronegative difference of greater than 1.7 between the atoms

Polar and nonpolar molecules do not mix unless...

Another molecule is added that has both polar and nonpolar sections.

Why do atoms form bonds with other atoms?

Atoms form bonds with other atoms so that they will have a full octet of valence electrons and because atoms are often more stable when bonded to other atoms.

Covalent Bonds

Bonds in which electrons are shared between atoms.

Which of the following examples is a compound containing an ionic bond? A. O2 B. H2O C. CaO D. CH4

CaO

What makes carbon special?

Carbon needs 4 valence electrons, which means that 2 carbon atoms can form a single bond, a double bond, or a triple bond. This makes carbon an extremely important element. Its ability to form so many bonds means it is in many compounds. In fact, all of life on Earth is based around carbon.

Chemical Bond

Chemical bonds hold atoms together. An attraction between atoms.

Which type of bond forms between S and H?

Covalent 0.4 is less than 1.7, so it is a covalent bond.

For what kind of bond are electrons shared by two atoms?

Covalent For covalent bonds, an electron is shared.

What kind of bond forms between two chlorine atoms?

Covalent They have the same electronegativity, so they form a covalent bond.

What kind of bond is present in HCE?

Covalent Bond

Put the elements in order, from lowest electronegativity to highest. K, Cs, N, Si, O, Na, F

Cs, K, Na, Si, N, O, F

Molecules form when atoms share __________________.

Electrons

Ionic Bonds

Formed when one or more electrons are transferred from one atom to another

Polar

Having an unbalanced arrangement of charge. Polar molecules have two oppositely charged ends, or poles. Another way to describe polar molecules is to say that they have a dipole moment.

Hydrogen Bonding and DNA

Hydrogen bonding plays an important role in the human body because it holds together the genetic information that every cell contains. This information, called DNA, contains the instructions for how to make everything in your body. DNA is a complex molecule that is shaped like a winding ladder. The two sides of the ladder are held together by hydrogen bonds.

How does molecular shape affect polarity?

If the molecule contains nonpolar bonds, a bent shape will make it polar.

Dipole-Dipole Forces

Intermolecular attractive forces between the negative end of one polar molecule and the positive end of another polar molecule. Dipole-dipole forces are intermolecular forces between two polar molecules.

What kind of bond forms between a fluorine atom and a magnesium atom?

Ionic Fluorine and magnesium have very different electronegativities.

What kind of bond usually forms between a metal and a nonmetal?

Ionic Metals and nonmetals usually have large differences in electronegativity, so they form ionic bonds.

Which type of bond forms between Cl and Mg?

Ionic The electronegativity difference between them is 1.8, so it is an ionic bond.

How does hydrogen bonding affect water?

It makes water hold together Hydrogen bonds hold water molecules together.

What must be true for a molecule to be polar?

It must contain polar bonds Polar molecules always have polar bonds.

The electronegativity difference between two atoms determines the electron sharing between those atoms.

Just as an older child would be more capable of taking a toy from a smaller child than the other way around, an atom with a much higher electronegativity is more likely to take an electron from an atom with a much lower electronegativity. The bigger the electronegativity difference between two atoms, the more unequal the sharing of electrons. If the difference is large enough, the atoms don't even share the electron. The atom with high electronegativity takes the electron from the atom with low electronegativity, and an ionic bond is formed instead of a covalent bond.

Where does hydrogen bonding most often occur?

Living things; for example, plants.

What kind of bond forms between silver (Ag) atoms?

Metallic bonds form between two or more metal atoms.

Which element forms a covalent bond with F?

N Rb and F have an electronegativity difference of 3.2, so they form an ionic bond.

Does the molecule have polar bonds? Example: A bond between two Cl molecules

No The chlorine atoms have the same electronegativity, so they do not have a polar bond.

Is the molecule polar or nonpolar? Example: A bond between two Cl molecules

Nonpolar The molecule does not have polar bonds, so it is nonpolar.

Is the BH3 molecule polar or nonpolar?

Nonpolar There are polar bonds, but they all cancel each other out, so the molecule is nonpolar.

In water, hydrogen (H) and oxygen (O) share electrons in covalent bonds. But which pulls harder on the electrons in the bond — H or O?

Oxygen O has higher electronegativity, so it pulls harder on the electrons.

Which atom would need to share more than 1 electron to have a full octet? Fluorine (F) Bromine (Br) Iodine (I) Oxygen (O)

Oxygen (O)

The bonds in water are between hydrogen (H) and oxygen (O) atoms. There is a large difference in negativity between hydrogen and water, so the bonds are very ___________.

Polar

Is the H2S molecule as a whole polar or nonpolar?

Polar The polar bonds do not cancel each other out, so it is a polar molecule.

Polar Covalent and Nonpolar Covalent Examples:

Polar Covalent H-F H-N C-N Nonpolar Covalent F-F Cl-Cl N-N

Which element has a higher electronegativity? Hydrogen (H) Sulfur (S)

Sulfur (S) Sulfur is more to the right on the periodic table, and electronegativity increases left to right.

Why does an ionic bond form after an electron is stolen?

The two atoms are attracted to each other.

What happens when two atoms with different electronegativities form a covalent bond?

They form a polar bond A difference in electronegativity leads to a polar bond.

Why do atom with less than 7 valence electrons bond with other atoms?

To get a stable arrangement of electrons

What force holds together substances made of nonpolar molecules?

Van der Waals forces

Van der Waals Forces

Weak intermolecular attractions or repulsions. The Van der Waals forces are much weaker than dipole-dipole forces or hydrogen bonds. A general explanation of Van der Waals forces is that there are fluctuations within the electron cloud in an atom. In other words, at any point in time, there are more electrons on one side of the atom than the other, so it's possible there are parts that are sometimes slightly negative or slightly positive. These changes can cause a molecule to behave as if it's slightly polar.

The sharing of electrons in covalent bonds is only equal if the 2 atoms are of the same element.

When 2 atoms of the same element share an electron, they share it equally in a purely covalent bond. Earlier, you learned that the 2 nitrogen atoms within a nitrogen molecule divide the 6 shared electrons evenly between them.

Does the molecule BH3 contain polar covalent bonds between the boron (B) atom and each hydrogen (H) atom?

Yes B and H have different electronegativities, so they form polar bonds.

Does the molecule H2S contain polar covalent bonds between each hydrogen (H) atom and the sulfur (S) atom?

Yes S and H have somewhat different electronegativities, so they form a polar covalent bond.

Could these two H-F molecules be held together by hydrogen bonding?

Yes; they could form a hydrogen bond Hydrogen bonding occurs whenever a hydrogen atom bonded to an oxygen (O), a nitrogen (N), or a fluorine (F) atom is attracted to another oxygen, nitrogen, or fluorine atom.

You can use placement on the periodic table to determine whether a bond is covalent or ionic.

You can use the 1.7 rule to determine if a bond is covalent or ionic, but you can also just look at the periodic table. If two elements are near each other on the periodic table, they probably have a covalent bond. If they are very far apart, they probably have an ionic bond. Sort the following pairs of atoms based on what bond would form between them.