Why some compounds are possible and others impossible? Why is there H2O, but not HO2? Why is there CO2, but not C2O? Why is there H2, but not H?

Why is there NaCl, but not Na2Cl or NaCl2?

At the end of this lesson, you will be able to: Explain why inert gases are stable Explain conditions for the formation of chemical

bonds State the two different types of chemical bonds

Human nature reflects chemical bonding Most people need to make connections with others. But not anyone will do. How do we select people that we can bond with?

What are the criteria that we set? Is it possible to predict the bonds that one person will

make in his/her life?

But atoms are not so complicated How do atoms bond with one another? Why do they form chemical bonds? Why inert gases can live on their own forever without making a single connection in their lives

What happens in a chemical reaction? Old bonds are broken and new ones are made. The result? Products, completely different from the reactants

Activity to discover how atoms bond with one another Two kinds of bonding: I: Between metal and non-metal atoms II: Between non-metal and non-metal atoms Ways that bonds can form: I: By sharing of electrons II: By transfer of electrons #p #e Group task: Using the element cards, periodic table and one cent coins,

combine any two elements to form a compound that fulfills the octet rule for all atoms involved. You need only show the valence electron shell

At the end of this lesson, you will be able to: explain formation of ions write electron arrangements for the ions formed explain formation of ionic bond

illustrate electron arrangement of an ionic bond, illustrate formation of ionic bond.

Stability of atoms What is stability of atoms? How do we know if an atom is stable or not?

Two ways chemical bonds can form Bond forming involves valence electrons on two atoms by Electron transfer One species donates/lose or release all its valence electrons The other species accepts/ gains or receives electrons Electron sharing One or more pairs of electrons will be shared between 2 atoms

Ionic bonding Transfer of electrons So named because this bond is between ions Atoms become ions because by losing/accepting e,

their #p #e Creates one positive ion cation When an atom loses electrons, it becomes positive

One negative ion anion When an atom gains electrons, it becomes negative

Filled shells by gain or loss of electrons

Gain electron outer shell full Lose electron inner shell full

Rules to predict ion charge Metals lose e cations Cation Charge = # of e released

Equation of the process: Na Na+ + e- , Mg Mg2+ + 2e-

Non-metals gain e anions Anion Charge = # of e received Equation of the process: Cl + e- Cl , O + 2e- O2-

Sodium chloride

Na loses electron

Cl gains electron

Composition of ionic compound depends on ionic charge (group number) Charges must balance: ions are charged but compounds are neutral Total cation charges = total anion charges One Ca2+ two F-

Determining formulae Overall charge must be neutral Metal ion first, nonmetal ion second

Ax B y

y+

x-

Coefficient of metal = charge on nonmetal Coefficient of nonmetal = charge on metal x and y are shown with lowest common denominator in most

cases. Calcium oxide is CaO not Ca2O2

Guided Practice Draw electronic structure of atoms write electron

arrangement draw what happens (e transfer) draw what happens after the transfer of e Lithium + fluorine Sodium + oxygen Aluminium and chlorine

2Na + Cl2 2NaCl When metal and non-metal bond, the metal has very low

electronegativity so they will lose their electrons to the nonmetal which has higher electronegativity

Ionic compounds Formed when ions of opposite charges are held by

strong electrostatic forces of attraction Because of this very strong attraction, a lot of energy is needed to separate the ions. Therefore mpt and bpt are very high Arranged in an orderly and compact three-dimensional network Very soluble in water and polar solvents because they can form bonds with water and polar solvents

Physical properties of ionic compounds

Hard, rigid solids at room temperature High melting point Dissolve in polar solvents (if soluble) Solutions conduct electricity (all soluble ionic compounds are electrolytes electricity-conducting soln) Closely packed dense structures

(Compare how metals conduct electricity)

Predicting formula of ionic compounds Na, O Na Na+ + e O + 2e O2-

2Na + O Na2O

A more accurate representation: Na Na+ + e O2 + 4e 2O2-

4Na + O2 2Na2O

Covalent bonds Non-metals have similar electronegativities, neither can take electrons away from the other Hence they are forced to share electrons

Explain why ionic compounds are formed when a metal bonds with a nonmetal but covalent compounds are formed when two nonmetals bond. When a metal bonds with a nonmetal, electrons are

transferred from the metal to the nonmetal because metals have very low electronegativities and nonmetals have high electronegativities. Because nonmetals tend to have similarly high electronegativities, neither atom can take electrons from the other, forcing them to share electrons.

Covalent bonds and compounds Covalent bonds can be formed between Atoms of the same element elements Atoms of different elements compound Three types of covalent bonds Single bond one pair of e shared between 2 atoms Double bond two pairs of electrons shared between 2 atoms Triple bond - three pairs of electrons shared between 2 atoms

How many valence electrons will atoms share? It depends on how many they need (valency) Alone each has seven, each need one more In order to get one more, Cl needs to share one

Number of bonds = 8 (no of valence electrons) Each covalent bond is a pair of electrons shared

Covalent bonds between unlike elements Oxygen and hydrogen Oxygen: No of bonds formed = 8 6 = 2 Hydrogen: No of bonds formed = 2 1 = 1 Predict Lewis structure of water

Try drawing the Lewis structure for these Use this equation to predict the # of bonds formed and

the molecular formula of the compound: No of bonds formed//valency = 8 (or 2) - #valence e Carbon and oxygen Nitrogen and nitrogen Carbon and chlorine Nitrogen and hydrogen

Bond order increases as valence electron total decreasesMolecule

# valence e

Total number of electrons in molecule

Bond order

F-F O=O NN

7 6 5

14 12 10

1 2 3

Practice P and Q are two elements with proton numbers 6 and 9 respectively. Draw the Lewis diagram for the formation of compounds between Q and H Q and P

Diatomic molecules

Predicting formula of covalent compounds M (Gp 14) and N (Gp 16) M: valency 4 N: valency 2

M2N4 Therefore, compound formed: MN2

element

No of valence e Valency

Gp 14 Gp 15 Gp 16 Gp 17

4 5 6 7

4 3 2 1

M (Gp 15) and N (Gp 17)/ (Gp 1) M: valency 3 N: valency 1

MN3 Therefore, compound formed: MN3

Draw/ illustrate Compare between ionic bonding and covalent bonding in terms of Aim or final result of bonding

What happened to valence electrons Types of particles formed as a result of bonding Type of attractive forces between particles after bonding

Properties of simple moleculesWeak interparticle forces of attraction (van der Waals) low m.pt, b.ptInterparticle forces of attraction -Formed between particles (in this case, molecules) -Temporary, forms only when particles are close to each other -Disappears when particles move further apart Covalent bond (a chemical bond) -Formed between atoms Weak interparticle in a molecule

forces of attraction ~ -Broken only only very little energy during a chemical reaction required to overcome -Formed these forces only during achemical reaction

Simple covalent and giant covalent

Giant covalent structure - diamond

Summary A+BC+D Reactants : one or all not stable Hence undergo reaction (form chemical bonds, sometimes

break existing bonds) to become more stable Products: More stable than reactants, after formation of ionic/ covalent bonds Ionic bonding// ions are formed Covalent bonding // molecules are formed

Explaining formation of ionic bond Na + O2 // sodium unstable but oxygen stable

A sodium atom (2.8.1) achieves the stable octet electron arrangement after it loses its valence e to form a sodium ion, Na+ // Na Na+ + e An oxygen atom with an e arrangement of 2.6 achieves the stable octet electron arrangement after it accepts 2 valence e from 2 sodium atoms to form an oxide ion, O2//O

+ 2e O2-

The electrostatic force of attraction between the

oppositely-charged sodium and oxide ions forms the ionic bond.

Explaining formation of covalent bond Formation of ammonia molecule (NH3 ) Nitrogen has an electron arrangement of 2.5 It needs to share 3 valence electrons in order to achieve a stable octet

electron arrangement. Hydrogen has an electron arrangement of 1 It needs to share 1 valence e to achieve a stable duplet electron arrangement One nitrogen atom contributes three of its valence electrons to be shared with three hydrogen atoms, each sharing its only electron to form three single covalent bonds. By sharing three valence e, N atom achieves the stable octet e arrangement. Each H atom achieves the stable duplet e arrangement by sharing its only electron.

Practice (ex from pink book)

Chemical reactions that you will encounter Synthesis reaction

Bird eats worm fat bird Two or more simple substances combine to form a complex

product Eg, Eg, 2Mg + O2 2MgO

Chemical reactions that you will encounter Decomposition reaction

Egg hatches egg shell + organism A complex substances breaks down to form 2 or more

simpler substances Eg,

Chemical reactions that you will encounter Single replacement reaction

John attends a party, meets Anna and Brad, steals Anna

from Brad, leaving Brad alone When one reactant has greater affinity for an ion, it will steal the ion from its partner Eg,

Chemical reactions that you will encounter Double displacement/replacement reaction

Exchange hats/ partners Eg,