Dr. Marwa Eid 1

Chemical Bonds - attractive force that holds atoms or ions together - Chemical bonding are classified into 3 types ionic, covalent, metallic

Chemical Bonding Electronegativity – the tendency of an atom to attract electrons from a neighboring atom. Hey! I find your electrons attractive! Get lost, loser!

Electronegativity increases as you move from left to right. Electronegativity decreases as you move down each column.

Valence Electrons – electrons in the outermost occupied energy level. - Valence electrons can be represented by “dots” drawn around the atom.

Atom – the smallest unit of matter Helium atom 6

Electron Shells a)Atomic number = number of Electrons 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 7

Electrons are placed in shells according to rules: The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons. 8

Why are electrons important? Elements have different electron configurations  different electron configurations mean different levels of bonding 9

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons 10

Bonding Elements that do not have a complete octet, tend to react. When the elements react bonds are formed. 11

Some Common Ions 12

Chemical bonds: an attempt to fill electron shells 1.Ionic bonds 2.Covalent bonds 3.Metallic bonds 13

14

IONIC BOND A bond formed between two oppositely ions by the transfer of electrons. Each element (now an ion) will have a complete octet after the transfer of electrons 15

When the electronegativities of two atoms are quite different from each other: One atom loses an electron (or electrons) The other atom gains an electron (or electrons) This results in an Ionic Bond.

IONIC BOND 17

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+ 18

Some Typical Ions with Positive Charges (Cations) Group 1Group 2Group 13 H + Mg 2+ Al 3+ Li + Ca 2+ Na + Sr 2+ K + Ba 2+ 19

Learning Check A. Number of valence electrons in aluminum 1) 1 e - 2) 2 e - 3) 3 e - B. Change in electrons for octet in aluminum 1) lose 3e - 2) gain 3 e - 3) gain 5 e - C.Ionic charge of aluminum 1) 3- 2) 5- 3)

Solution A. Number of valence electrons in aluminum 3) 3 e - B. Change in aluminum electrons for octet 1) lose 3e - C.Ionic charge of aluminum (13) 3)

22

FK 23

FK 24

FK 25

FK 26

FK 27

FK 28

FK 29

FK + _ 30

FK + _ The compound potassium fluoride consists of potassium (K + ) ions and fluoride (F - ) ions 31

FK + _ The ionic bond is the attraction between the positive K + ion and the negative F - ion 32

33

 COVALENT BOND Bond formed by the sharing of electrons 34

Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Stable non-ionizing particles. Examples; O 2, CO 2, C 2 H 6, H 2 O 35

Covalent BondNon-polarPolar 36

when electrons are shared equally Non-polar Covalent Bonds H 2 or Cl 2 37

Cl circle the electrons for each atom that completes their octets The octet is achieved by each atom sharing the electron pair in the middle 38

Cl circle the electrons for each atom that completes their octets It is a single bonding 39 This is the bonding pair

Cl Single bonds are abbreviated with a dash 40

Oxygen Atom Oxygen Molecule (O 2 ) Oxygen Molecule (O 2 ) 41

Bonds in all the polyatomic ions and diatomics are all covalent bonds 42

when electrons are shared but shared unequally Polar Covalent Bonds H2OH2O 43

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen. 44

1. Define the following: a. Ionic bond b. Covalent bond Compare between polar and non-polar covalent bond 45

METALLIC BOND 46

METALLIC BOND Bond found in metals; holds metal atoms together very strongly 47

Metallic Bond A lattice of positive ions in a sea of electrons Formed between atoms of metallic elements Electron cloud around atoms Examples; Na, Fe, Al, Au, Co 48

Sea of Electrons 49

This electrostatic attraction is called metallic bonding and is the reason why the positive metal ions do not repel each other. The outer shell electrons separate from their atoms and become delocalized, creating a ‘sea of electrons’. The atoms become positive ions and are attracted to these electrons. metal atoms sea of free electrons metal ions Metallic bonding 50

Properties of Metallic Bonds Good electrical conductors - free electrons can move through the lattice carrying charge (GR). Conduct heat because of free electrons Lusterous – absorb and emit light in regular pattern due to free electrons 51

Malleable (can be hammered into different shapes) and ductile ( can be drawn into wires) – not in rigid position so ions can be shaped and drawn into wires 52 Properties of Metallic Bonds