Atoms have NO overall charge

• ATOMS DO NOT HAVE A CHARGE BECAUSE THEY HAVE AN EQUAL NUMBER OF PROTONS AND ELECTRONS WHO CHARGES EXACTLY CANCEL! • A CHLORINE ATOM HAS 17 PROTONS, WHICH MEANS IT HAS 17 ELECTRONS ALSO…• NEUTRONS HAVE NO CHARGE. •BUT…if an electron is removed from an element then things change…

7 protonsNitrogen (N)7 electrons

Valence Electrons: an electron in the outermost energy level of an atom. There can only be 2 electrons in the first energy level.The second energy level can hold 8 electrons & every level after that.

E

E

EE

E

E

E

8 e-’s 8 e-’s

2 e-’s

Nitrogen’s electrons only fill up five of the second shell. So this means there are 5 valence electrons for Nitrogen (the same as the group they are found in on the periodic table – 5A)

Atoms of metallic elements tend to lose their valence electrons leaving a complete octet in the next lowest energy level. Atoms of some nonmetallic elements tend to gain electrons or share electrons with another nonmetallic element to achieve a complete octet.

An octet is a set of 8. An energy level can hold up to 8 electrons in its outer most energy level.

• Ionic Bonds form when elements do not have complete sets of valence electrons. This usually occurs between a metal cation and a nonmetal anion.• Some elements achieve stable electron configurations through the transfer of electrons between atoms.• Transfer of electrons takes place when one electron is donated or accepted from one atom to another.

• Formation of Ionic Bonds= When an atom gains or loses an electron it becomes an ion• An ion is a charged particle which can bond with another charged particle• A CATION is a positively charged atom, such as Na+ or H+ or Be2+ , etc.• A ANION is a negatively charged atom, such as I-, Cl-, S2-, N3-, etc. • Sharers, such as Carbon usually bond covalently and share electrons.

1. Would Lithium (Li) be a cation or anion?

2. Would Hydrogen (H) be a cation or anion?

3. Would Nitrogen (N) be a cation or anion?

4. Would Florine (F) be a cation or anion?

5. Boron?6. Aluminum?7. Calcium?

Cation + 1

Cation +1

Anion 3-

Anion 1-

Cation 3+

Cation 3+

Cation 2+

• An electron can move to a higher energy level when an atom absorbs energy. • The amount of energy used to remove and electron is called IONIZATION ENERGY• The Trends are as follows on the periodic table.

Generally increases

Gene

rally

dec

reas

es

•Ionization: the process of adding electrons to or removing electrons from an atom or a group of atoms.

- Ionic Bonds

Properties of Ionic Compounds• In general, ionic compounds are hard, brittle

crystals that have high melting points. When dissolved in water or melted, they conduct electricity.

- Ionic Bonds

Ions and Ionic Bonds• When an atom loses an electron, it loses a

negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion.

If the first energy level only has two electrons then electrons are located in the next energy level. For example, Sodium

p = 11e= 11n= 12

After the first two electrons take up the first energy level, 9 more electrons are located in different energy levels.Only 8 electrons can fill up the second energy level. This is called the octet rule.So the last electron is located in the last level, all by itself! This is what gives sodium a (+1) charge when it becomes ionized.

Sodium (Na)

• When the outermost energy level of an atom is filled with electrons, the atom is stable and not likely to react.• An electron dot diagram is a model of an atom in which each dot represents a valence electrons.• Atoms can bond with one another by switching, sharing, or exchanging electrons with one another.

- Atoms, Bonding, and the Periodic Table

Valence Electrons and Bonding• The number of valence electrons in an atom of

an element determines many properties of that element, including the ways in which the atom can bond with other atoms.

- Atoms, Bonding, and the Periodic Table

The Periodic Table• As the number of protons (atomic number)

increases, the number of electrons also increases. As a result, the properties of the elements change in a regular way across a period.

- Ionic Bonds

Ions and Ionic Bonds• Ionic bonds form as a result of the attraction

between positive and negative ions.

Let’s Practice!

# of Valence Electrons: ______

Charge as an Ion: _________

# of Valence Electrons: ______

Charge as an Ion: _________

# of Valence Electrons: ______

Charge as an Ion: _________

# of Valence Electrons: ______

Charge as an Ion: _________

# of Valence Electrons: ______

Charge as an Ion: _________

# of Valence Electrons: ______

Charge as an Ion: _________

What is a covalent bond

• A covalent bond occurs when atoms share electrons

• Covalent bonds occur between two non-metals

• Valence electrons play a role in covalent bonds

Molecules and Molecular Compounds

• Molecule – a neutral group of atoms joined together by a covalent bond.

• Diatomic molecule – a molecule consisting 2 of the same element. Example: O2

• Molecular compound – a compound composed of molecules. (covalently bonded atoms).

The Diatomic Elements• The elements Hydrogen, Nitrogen, Fluorine, Oxygen,

Iodine, Chlorine, and Bromine are always found as diatomic molecules:

• HONClFIBr (say HONKLE-fibber) • BrINClHOF (say Brinckle-hoff) • I Have No Bright Or Clever Friends • There are seven such elements. The first one is the first

element Hydrogen; the rest form a 7 on the periodic table: N, O, F across, then going down Cl, Br, I.

Characteristics of Molecular Compounds (elements that are bonded covalently)

• Lower melting points and boiling points than ionic compounds.

• Most are gases or liquids at room temperature.

• Are composed of atoms of 2 or more nonmetals.

Molecular Formulas

• A molecular formula shows how many atoms of each element a molecule contains.

Ex: H2O has 2 hydrogen atoms and 1 oxygen atom

• You can represent a molecule by its molecular formula, structural formula, space-filling molecular model, perspective drawing or by a ball-and-stick molecular model.

Different ways to represent a molecule:

Structural formula Perspective drawing

Space-filling molecular model Ball-and-stick molecular model

Molecular Formula

NH3

What happens in a covalent bond• In a covalent compound, electrons are shared between atoms

to form a covalent bond in order that each atom in the compound has a share in the number of electrons required to provide a stable, Noble Gas, electronic configuration (octet rule).

• Each atom “thinks” it has a full outer shell containing 8 valence electrons

• The sharing of electrons is what makes the bond and holds the atoms together

Lewis Structures and Covalent Bonds

• Electrons in the Lewis Structure (electron dot diagram) are paired to show the bonding pair of electrons.

• Often the shared pair of electrons forming the covalent bond is circled

• Sometimes the bond itself is shown with a dash (-)• A pair of valence electrons that is not shared between atoms

is called an unshared pair, lone pair or non-bonding pair.

Water – Is an example of a covalent compound.

• Hydrogen needs 2 electrons to fill its outermost shell

• Oxygen needs two electrons to fill its outermost shell

Lewis Structure of Water (single covalent bonds)

http://web.visionlearning.com/custom/chemistry/animations/CHE1.7-an-H2Obond.shtml

Lewis Structure of Carbon Dioxide: CO2 (Double covalent bonds)

• Carbon has four valence electrons, and oxygen has six.

• Each pair of shared electrons forms a single bond

• A bond that involves two shared pairs of electrons is called a double covalent bond.

Lewis Structure of Nitrogen (triple covalent bonds)

T

A bond formed by sharing 3 pairs of electrons is called a triple covalent bond.

+ =

You Try It

• What would the formula be for a compound containing carbon and fluorine

• What is the formula for a compound containing nitrogen and oxygen

• Carbon and hydrogen?• Antimony and bromine?• Chlorine and oxygen?