Chemical BondsChemical Bonds

Atom – the smallest unit of matter “indivisible”

Heliumatom

electron shellselectron shellsa)a) Atomic number = number of ElectronsAtomic number = number of Electrons

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

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

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 Why are electrons important?important?

1)1) Elements have different electron Elements have different electron configurationsconfigurations different electron configurations mean different electron configurations mean

different levels of bondingdifferent levels of bonding

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

Chemical bonds: an attempt to fill electron Chemical bonds: an attempt to fill electron shellsshells

1.1. Ionic bonds Ionic bonds 2.2. Covalent bonds Covalent bonds 3.3. Metallic bondsMetallic bonds

Learning Check Learning Check

IONIC BONDIONIC BONDbond formed bond formed

between between two ions by the two ions by the

transfer transfer of of electronselectrons

Formation of Ions from Formation of Ions from MetalsMetals

Ionic compoundsIonic compounds result when result when metalsmetals react react with with nonmetalsnonmetals

Metals Metals loselose electrons to match the electrons to match the number of number of valence electrons valence electrons of their nearest noble gasof their nearest noble gas

Positive ionsPositive ions formform when when the number of the number of electrons are electrons are lessless than the number of protons than the number of protons

Group 1 metals Group 1 metals ion ion 1+1+

Group 2 metals Group 2 metals ion ion 2+2+

Group 13 metals Group 13 metals ion ion 3+3+

Formation of Sodium Formation of Sodium IonIon

Formation of Formation of Magnesium IonMagnesium Ion

Some Typical Ions with Some Typical Ions with Positive Charges Positive Charges

(Cations)(Cations)Group 1Group 1 Group 2Group 2 Group 13Group 13

HH++ MgMg2+2+ AlAl3+3+

LiLi++ CaCa2+2+

NaNa++ SrSr2+2+

KK++ BaBa2+2+

Learning Check Learning Check A. Number of valence electrons in A. Number of valence electrons in

aluminum?aluminum?

B. Change in electrons number to be stable?B. Change in electrons number to be stable?

C.C. Ionic charge of aluminum? Ionic charge of aluminum?

Learning CheckLearning CheckGive the ionic charge for each of the following:Give the ionic charge for each of the following:A. 12 pA. 12 p+ + and 10 e and 10 e--

B. 50pB. 50p++ and 46 e- and 46 e-

C. 15 pC. 15 p++ and 18e- and 18e-

Ions from Nonmetal IonsIons from Nonmetal IonsIn ionic compounds, nonmetals in 15, In ionic compounds, nonmetals in 15,

16, and 17 gain electrons from metals 16, and 17 gain electrons from metals

Nonmetal add electrons to achieve the Nonmetal add electrons to achieve the octet arrangement octet arrangement

Nonmetal ionic charge: Nonmetal ionic charge:

3-, 2-, or 1-3-, 2-, or 1-

Fluoride IonFluoride Ion

Ionic BondIonic Bond

Between atoms of metals and nonmetals with Between atoms of metals and nonmetals with very different electronegativityvery different electronegativity

Bond formed by transfer of electronsBond formed by transfer of electronsProduce charged ions; theregore conductors. Produce charged ions; theregore conductors. Have high melting point.Have high melting point.Examples; NaCl, CaClExamples; NaCl, CaCl22, K, K22OO

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.

COVALENT BONDCOVALENT BONDbond formed by bond formed by the the sharing sharing of of

electronselectrons

Covalent BondCovalent Bond

Between nonmetallic elements of similar Between nonmetallic elements of similar electronegativity.electronegativity.

Formed by sharing electron pairsFormed by sharing electron pairsStable non-ionizing particles, they are not Stable non-ionizing particles, they are not

conductors at any stateconductors at any stateExamples; OExamples; O22, CO, CO22, C, C22HH66, H, H22O, SiCO, SiC

when when electrons are electrons are

shared shared equallyequally

NONPOLAR COVALENT BONDS

H2 or Cl2

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

Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom

Oxygen Molecule (OOxygen Molecule (O22))

when when electrons are electrons are shared but shared but

shared shared unequallyunequally

POLAR COVALENT BONDS

H2O

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

Learning Check Learning Check A.A. Which of the following compounds are covalent?Which of the following compounds are covalent?

1)1) NaBrNaBr 2) CH2) CH44 3) SiO3) SiO22 4) O4) O22

5) MgCl5) MgCl22 6) AlO6) AlO33 7) NH7) NH33 8) H8) H22SOSO44

B. Which of the following compounds are polar?B. Which of the following compounds are polar?

1) CO1) CO22 2) BH2) BH33 3) HCl3) HCl 4) CH4) CH44

METALLIC METALLIC BONDBOND

bond found in bond found in metals; holds metals; holds

metal metal atoms together atoms together

very stronglyvery strongly

Metallic BondMetallic Bond

Formed between atoms of metallic elementsFormed between atoms of metallic elementsElectron cloud around atoms Electron cloud around atoms Good conductors at all states, lustrous, very Good conductors at all states, lustrous, very

high melting pointshigh melting pointsExamples; Na, Fe, Al, Au, CoExamples; Na, Fe, Al, Au, Co

Ionic Bond, A Sea of Ionic Bond, A Sea of ElectronsElectrons

Metals Form AlloysMetals 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 Weights

Formula weight is the sum of the atomic Formula weight is the sum of the atomic masses.masses.

Example- COExample- CO22

Mass, C + O + O Mass, C + O + O 12.011 + 15.994 + 15.99412.011 + 15.994 + 15.99443.99943.999

PracticePractice Compute the mass of the following compounds round to Compute the mass of the following compounds round to

nearest tenth & state type of bond:nearest tenth & state type of bond: NaCl; NaCl; 23 + 35 = 58; Ionic Bond23 + 35 = 58; Ionic Bond CC22HH66; ; 24 + 6 = 30; Covalent Bond24 + 6 = 30; Covalent Bond Na(CONa(CO33))22; ; 23 + 2(12 + 3x16) = 123; Ionic & Covalent23 + 2(12 + 3x16) = 123; Ionic & Covalent