BondingIonic

Valence Electrons

The number of valence electrons in an atom of an element determines the many properties of that element, including the ways in which the Atom can bond with other atoms

electron shellsa) Atomic number = number of Electrons in a neutral atom

b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.

c) Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules:

1) The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons

C would like to N would like toO would like to

Gain 4 electronsGain 3 electronsGain 2 electrons

Why are electrons important?

1) Elements have different electron configurations different electron configurations mean different levels of

bonding As the number if protons (atomic number) increases, the number

of electrons also increases. As a result, the properties of the elements change in a predictable

way across a period.

Bohr Model

Lewis Electron Dot StructuresSymbols of atoms with dots to represent the valence-shell electrons

1 2 13 14 15 16 17 18

H He:

Li Be B C N O : F :Ne :

Na Mg Al Si P S :Cl :Ar :

Learning Check

A. X would be the electron dot formula for

1) Na 2) K 3) Al

B. X would be the electron dot formula

1) B 2) N 3) P

Chemical bonds: an attempt to fill electron shells

1. Ionic bonds

2. Covalent bonds

3. Metallic bonds

Ions and Ionic BondsYou and a friend walk past a market that sells apples for 40 cents each and pears for 50 cents each. You have 45 cents and want an apple. Your friend also has 45 cents but wants a pear.

Ions and Ionic BondsWhen 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.

Ions and Ionic Bonds

Ions are atoms that have lost or gained electrons.

Ionic Bonds form as a result of the attraction between positive and negative ions

Some Typical Ions with Positive Charges (Cations)

Group 1 Group 2 Group 13

H+ Mg2+ Al3+

Li+ Ca2+

Na+ Sr2+

K+ Ba2+

Learning Check

Give the ionic charge for each of the following:

A. 12 p+ and 10 e-

1) 0 2) 2+ 3) 2-

B. 50p+ and 46 e-

1) 2+ 2) 4+ 3) 4-

C. 15 p+ and 18e-

2) 3+ 2) 3- 3) 5-

Ionic Bond

Between atoms of metals and nonmetals with very different electronegativity

Bond formed by transfer of electrons

Produce charged ions all states. Conductors and have high melting point.

Examples; NaCl, CaCl2, K2O

Formation of Ions from Metals

Ionic compounds result when metals react with nonmetals

Metals lose electrons to match the number of valence

electrons of their nearest noble gas

Positive ions form when the number of electrons are less

than the number of protons

Group 1 metals ion 1+

Group 2 metals ion 2+

Group 13 metals ion 3+

Ions from Nonmetal Ions

In ionic compounds, nonmetals in 15, 16, and 17

gain electrons from metals

Nonmetal add electrons to achieve the octet

arrangement

Nonmetal ionic charge:

3-, 2-, or 1-

Ionic Bonds: One Big Greedy Thief Dog!

Ions and Ionic BondsIonic bonds form as a result of the attraction between positive and negative ions.

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

Properties of Ionic CompoundsIn general, ionic compounds are hard, brittle crystals that have high melting points.

When dissolved in

water or melted, they

conduct electricity.

BondingCovalent

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.

Oxygen Atom Oxygen Atom

Oxygen Molecule (O2)

Covalent Bond

Between nonmetallic elements of similar electronegativity.

(Between two nonmetals!)

Formed by sharing electron pairs

Stable, not conductors at any state

Examples; O2, CO2, C2H6, H2O, SiC

How Covalent Bonds FormThe force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.

- Covalent Bonds

How Covalent Bonds FormCovalent bonds usually form between atoms of

nonmetals.CO2

H20

NH3

- Covalent Bonds

How Covalent Bonds FormThe oxygen atom in water and the nitrogen atom in ammonia are each surrounded by eight electrons as a result of sharing electrons with hydrogen atoms.

- Covalent Bonds

How Covalent Bonds Form

In covalent bonds, atoms share two or more pairs of electrons

Except for hydrogen, the number of covalent bonds that nonmetal atoms can form equal the number of electrons needed to make a total of 8

Hydrogen needs only two.

- Covalent Bonds

How Covalent Bonds FormCovalent bonds can be double or triple bonds

Double bonds refer to two pairs of shared electrons. Triple bonds include three shared electrons

- Covalent Bonds

How Covalent Bonds FormAn oxygen molecule contains one double bond, while a carbon dioxide molecule has two double bonds. A nitrogen molecule contains one triple bond.

Equal and Unequal Sharing of Electrons

Nonpolar bonds: Electrons are equally shared.Fluorine forms a nonpolar bond with another fluorine atom.

Polar bonds: electrons are shared unequally In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar.

Polar Covalent Bonds: Unevenly matched, but willing to share.

Equal and Unequal Sharing of Electrons

A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

Molecular CompundsA molecular compound contains atoms that are covalently bonded

Compared to ionic compounds, molecular compounds generally have lower melting and boiling points and do not conduct electricity when dissolved in water

- Covalent Bonds

Comparing Molecular and Ionic Compounds

The table compares the melting points and boiling points of a few molecular compounds and ionic compounds..

- Covalent Bonds

Comparing Molecular and Ionic Compounds

Melting points of molecular compounds are lower than those of ionic compounds.

Interpreting Data:

Describe what the table reveals about the melting points of molecular compounds compared to those of ionic compounds.

- Covalent Bonds

Comparing Molecular and Ionic Compounds

Molecular compounds have weak attractive force between molecules, so less energy is needed to melt molecular compounds.

Inferring:

How can you account for the differences in melting points between molecular compounds and ionic compounds?

- Covalent Bonds

Comparing Molecular and Ionic Compounds

Boiling points of molecular compounds are lower than those of ionic compounds.

Interpreting Data:

How do the boiling points of the molecular and ionic compounds compare?

- Covalent Bonds

BondingMetallic

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Metallic Bond

Formed between atoms of metallic elements

Electron cloud around atoms

Good conductors at all states, lustrous, very high melting points

Examples; Na, Fe, Al, Au, Co

- Bonding in Metals

Metallic BondingA metal crystal consists of positively charged metal ions embedded in a “sea” of valence electrons.

Ionic Bond, A Sea of Electrons

Metals Form Alloys

Metals do not combine with metals to form compounds.They form an alloy, which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.\

Metals Form Alloys

Properties of AlloysConduct heat and electricityMalleableDuctileHave luster (shiny)Used in jewelry, mirrors, buildings, etc

Bonding Summary

Ionic bonds – between metals and nonmetals

Covalent bonds – between two nonmetals

Metallic bonds – between metals

 

Graphic Organizer

Attraction between oppositely charged ions

Feature Ionic BondPolar Covalent Bond

Nonpolar Covalent Bond

Metallic Bond

How Bond Forms

Charge on Bonded Atoms?

Example

Unequal sharing of electrons

Yes; positive or negative Yes; positive

O2 molecule

Equal sharing of electrons

Attraction between positive ions and surrounding electrons.

Yes, slightly positive or slightly negative

No

NaCl crystal (or other ionic compound)

H2O molecule (or other polar covalent molecule)

Calcium (or other metal)