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Chemical BondsHow Atoms Combine1The Atom

the smallest unit of matter indivisible

HeliumatomElectrons & shellsAtomic number = number of Electrons

Electrons vary in the amount of energy they have and they occur at certain energy levels or electron shells.

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

Why are electrons important?Chemical bonding involves electrons in the outermost energy level.

All Elements want to be stable & have 8 electrons in their valence level.

Octet RuleAtoms gain, lose or share electrons to have 8 electrons in their valence level.

Exception: He (duet rule)

C would like to N would like toO would like toGain 4 electronsGain 3 electronsGain 2 electronsChemical bondsAtoms attempt to fill electron shells.

When electrons are gained, lost or shared, an attractive force is formed called a BOND, which holds elements together.Ionic bonds (metal & non metal)Covalent bonds (2 non metals)Metallic bonds (2 metals)Ionic BondingOccurs between a metal and a non-metal.

Electrons are moved from one atom to another.

The charged particle that results is called an ION.IONSWhen an atom loses (or gives away) its electrons, it becomes a positively charged.

This is known as a CATION.

Alkali Metals commonly form positive ions.

IONSWhen an atom gains electrons, it becomes negatively charged.

This is known as an ANION.

Halogens commonly form negative ions.

Formation of Ions from Metals

Metals lose electrons to match the number of valence electrons of their nearest noble gasPositive 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+Formation of Sodium Ion Sodium atom Sodium ion Na e Na +

2-8-1 2-8 ( = Ne)

11 p+ 11 p+ 11 e- 10 e- 0 1+

Formation of Magnesium IonMagnesium atom Magnesium ion Mg 2e Mg2+ 2-8-2 2-8 (=Ne)

12 p+ 12 p+ 12 e- 10 e- 0 2+

Typical Ions with Positive Charges (Cations)Group 1Group 2Group 13H+Mg2+Al3+Li+Ca2+Na+Sr2+K+Ba2+

Learning Check A. Number of valence electrons in aluminum1) 1 e- 2) 2 e-3) 3 e-

B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5 e-

C.Ionic charge of aluminum 1) 3- 2) 5- 3) 3+ Solution A. Number of valence electrons in aluminum3) 3 e-

B. Change in electrons for octet1) lose 3e-

C.Ionic charge of aluminum 3) 3+ Learning CheckGive the ionic charge for each of the following:A. 12 p+ and 10 e-1) 02) 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- Formation of Ions from NonmetalsIn ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals Nonmetals gain electrons to achieve a stable octet Nonmetal ionic charge: -3, -2, or -1

Fluoride Ionunpaired electron octet 1 - : F + e: F :

2-7 2-8 (= Ne) 9 p+ 9 p+ 9 e- 10 e- 0 -1 ionic chargeIONS & BondsPositive ions attract negative ions to form ionic bonds.

Ionic Bond: formed between two ions by the transfer of electronsIonic BondElectron Stealers

Between atoms of metals and nonmetals.

Strong bond formed by transfer of electrons

Examples: NaCl, CaCl2, K2O

Ionic Bond PropertiesCrystal lattice: repeating 3D pattern

Ionic Bond PropertiesStrong attraction between ions result in brittleness.

Ionic Bond PropertiesHigh melting points & usually solid at room temperature.

Ionic Bond PropertiesSoluble

Good Conductors

Ionic Bonds: One Big Greedy Thief Dog!

polyatomic ionsA covalently bonded group of atoms acting as one that have a positive or negative charge.

http://web.jjay.cuny.edu/~acarpi/NSC/salt.htm

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.

Oxidation NumbersThe number of electrons that an element can lose, gain or share is called the OXIDATION NUMBER.

Some elements have more than one oxidation number, example Fe +2 or Fe+3

Covalent BondBetween 2 or more nonmetal elements.Formed by sharing electron pairs.

Covalent BondSharers Tend to be gases, liquids & soft solidsForm moleculesThey are not conductors at any state.Examples; O2, CO2, C2H6

Smallest unit of a covalently bonded compound is called: molecule

Covalent Bonds

Electrons are shared equallyNONPOLAR COVALENT BONDSH2 or Cl2

Covalent bonds

Two atoms can share one or more pairs of outer-shell electrons.

Diatomic MoleculesSome elements exist in nature as covalent bonds.Composed of only 2 atoms

Diatomic MoleculesNonmetals called the Heavenly 7

Electrons are shared but shared unequallyPOLAR COVALENT BONDSH2O

Polar Covalent Bonds Unevenly matched, but willing to share

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

Metallic BondFormed between atoms of metallic elementsMetal atoms become cations surrounded by a pool of electronsGood conductors at all states, lustrous, very high melting pointsExamples; Na, Fe, Al, Au, Co

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

Metallic BondAttraction between a metal cation and shared electrons.

Metals Form Alloys

Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.Formula WeightsFormula weight is the sum of the atomic masses.Example- CO2Mass, C + O + O 12.011 + 15.994 + 15.99443.999 PracticeCompute the mass of the following compounds round to nearest tenth & state type of bond:NaCl; 23 + 35 = 58; Ionic BondC2H6; 24 + 6 = 30; Covalent BondNa(CO3)2; 23 + 2(12 + 3x16) = 123; Ionic & Covalent

The End