CHAPTER 6: CHEMICAL BONDS6.1 Ionic Bonding

STABLE ELECTRON CONFIGURATIONS If highest energy level of an atom is filled

with e-, the atom is stable and not likely to react

Chemical properties of an element depend on the number of valence electrons

Electron (Lewis) dot diagram = model in which each dot represents a valence electron

STABLE ELECTRON CONFIGURATIONS• Highest energy level of a noble gas

atom is completely filled• Noble gases have stable electron

configurations with 8 valence electrons (two electrons in helium).

• Elements tend to react to get electron configurations similar to noble gases

CHEMICAL BONDING http://www.youtube.com/watch?v=_M9khs87xQ8

CHEMICAL BONDING

Elements can get a stable electron configuration by transferring of electrons

Ex: A chlorine atom has one electron fewer than an argon atom, adding one electron would give chlorine a stable configuration

• Ex: A sodium atom has one more electron than a neon atom, removing one electron would give sodium a stable configuration.

CHEMICAL BONDING

When sodium reacts with chlorine, an electron is transferred from sodium atom to chlorine atom

Each atom ends up with a more stable electron arrangement than it had before transfer

CHEMICAL BONDS

Electron moves from Na to CL

FORMATION OF IONS

Ionic Bonds = transfer of electrons When an atom gains or loses an electron, the

number of protons does not equal number of electrons

Charge on the atom is not balanced, and atom is not neutral Ion = Atom that with positive or negative charge Charge on an ion is represented by a plus or a

minus sign Negative charge = anion Positive charge = cation

IONIC BONDS

Ex: Ion that forms when a chlorine atom gains an electron has 17 protons and 18 electrons• This ion has a charge of 1–.• The symbol for the ion is written Cl1–, or Cl– for

short. • Anions like the Cl– ion are named by using part of

the element name plus the suffix –ide. Thus, Cl– is called a chloride ion.

IONIC BONDS

Sodium ion has 11 protons and 10 electrons.• The sodium ion has a charge of 1+. • The symbol for the ion is written Na1+, or Na+ for

short. • An ion with a positive charge is a cation.• A cation uses the element name, as in the sodium

ion.

FORMATION OF IONIC BONDS

A particle with a negative charge will attract a particle with a positive charge

• Chemical bond = force that holds atoms or ions together as a unit

• Ionic bond =force that holds cations and anions together, forms when electrons are transferred from one atom to another (metal and non-metal)

IONIZATION ENERGY

Cations (+) form when electrons gain enough energy to escape from atoms

Energy allows electrons to overcome the attraction of the protons in the nucleus

Ionization energy = of energy used to remove an electrons

The lower the ionization energy, the easier it is to remove an electron from an atom

Ionization Energy

IONIC COMPOUNDS

Compounds that contain ionic bonds are ionic compounds, can be represented by chemical formulas• Chemical formula = shows what elements are in

a compound, and how many of each• Ex: Chemical formula for sodium chloride, NaCl,

indicates one sodium ion for each chloride ion in sodium chloride

BINARY IONIC COMPOUNDS

Compound made from only two elements is a binary compound

The names have a predictable pattern: The name of the cation followed by the name of

the anion. Examples: sodium chloride

DESCRIBING IONIC COMPOUNDS

Formula of an ionic compound describes the ratio of the ions in the compound

2 different compounds of copper and oxygen are below

Has to be at least two names to distinguish red copper oxide from black copper oxide.

POLYATOMIC IONS

Polyatomic ion = covalently bonded group of atoms that has a positive or negative charge

Most simple polyatomic ions are anions

What is the chemical formula for magnesium chloride?

Ionic Compounds

What is the chemical formula for magnesium chloride?

Ionic Compounds

MgCl2

NAMING IONIC COMPOUNDS

1. Write the name of the metal first and then the nonmetal.

2. Add an -ide ending to the non-metal3. Use Roman Numerals to indicate charge

on a transition metal Ionic compounds involving polyatomic

ions follow the same basic rule: 1. Write the name of the metal first, 2. Then the name of the polyatomic anions

CHAPTER 6: BONDINGSection 6.2 Covalent Bonds

COVALENT BOND

Sharing of valence electrons Non-metal and Non-metal Attraction between shared electrons

and the protons in each nucleus hold the atoms together in a covalent bond

COVALENT BOND

COVALENT BOND

SHARING ELECTRONS

When two atoms share one pair of electrons, the bond is called a single bond

Hydrogen atom has one electron, if had two electrons, it would have the same electron configuration as a helium atom

Two hydrogen atoms can achieve a stable electron configuration by sharing their electrons and forming a covalent bond

MOLECULES OF ELEMENTS

Molecule = neutral group of atoms that are joined together by one or more covalent bonds

Many nonmetal elements exist as diatomic molecules

Diatomic means “two atoms”

MEMORY TRICK:

Br-I-N-Cl-H-O-F

Brinclhof

Sounds like a German name.

There’s also:I Brought Clothes For Our New

Hamster… either way…

DIATOMIC MOLECULES

Bromine:

Iodine:

Nitrogen:

Chlorine:

Hydrogen:

Oxygen:

Fluorine:

MULTIPLE COVALENT BONDS

2 pairs of electrons shared = double bond 3 pairs of electrons shared = triple bond Nitrogen has five valence electrons. When the atoms in a nitrogen molecule

(N2) share three pairs of electrons, each atom has eight valence electrons

Each pair of shared electrons is represented by a long dash in the structural formula NN

UNEQUAL SHARING OF ELECTRONS

Polar covalent bond = atom with the greater attraction for electrons has a partial negative charge

Other atom has a partial positive charge Happens because the e- are closer to one

atom than the other (one atom attracts e- more)

Type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar

UNEQUAL SHARING OF ELECTRONS

Except for noble gases, elements on the right of the periodic table tend to have a greater attraction for electrons than elements on the left

Elements at the top of a group tend to have a greater attraction for electrons than elements at the bottom of a group have.

POLAR COVALENT BOND

Covalent bonds= atoms attract electrons equally and are shared equally

ATTRACTION BETWEEN MOLECULES

Attractions between polar molecules are stronger than attractions between nonpolar molecules

Bonds between polar molecule are stronger than non polar

NAMING COVALENT BONDS

Prefixes tell you how many of each atom you have

Prefix goes in front of the element name Mono- 1 Di -2 Tri – 3 Tetra -4 Penta – 5 Hexa – 6 Hepta – 7