chemical bonding

metallic bonding

electrostatic forces of attraction between the lattice of cations and delocalised electrons

strength of metallic bond is determined by

1. number of delocalised electrons (more electrons given out = stronger)

2. charge on the cation

3. radius of cation (smaller = stronger attraction)

Na⁺ vs Mg²⁺ , which has higher MP

• Na has one delocalised electron per atom while Mg has 2 delocalised electrons per atom

• the charge of Mg is more than Na

• Radius of Na is larger than Mg

• Mg has stronger metallic bonding than Na , requiring more energy to overcome strong metallic bonds

• Mg has higher MP

physical properties of metals

1. good conductor of electricity

2. good thermal conductivity

3. malleable (shaped under pressure)

4. ductile (drawn into thread)

5. high melting point

metals are good conductors of electricity because

delocalised electrons are highly mobile , can move through the metal structure in response to an applied voltage

• application : electrical wires

metals are good thermal conductors because

delocalised electrons and closely packed ions enable efficient transfer of heat energy

• cooking utensils

malleable + ductile (metallic bonding)

movement of delocalised electrons is non directional and random through the cation lattice , the metallic bond remains intact while the conformation changes under applied pressure

why do metals have high MP

a lot of energy is needed to overcome the strong metallic bonds

alloy

mixture of 2 or more elements (including carbon)

• metal x (non metal/metal)

the addition of another element disrupts the regular arrangement of metal cations in metal lattice

alloy characteristics

1. stronger

2. more resistant to corrosion

3. more chemically stable

because : the addition of another element disrupts the regular arrangement of metal cations in metal lattice

steel alloy

• iron + carbon + other elements

• high tensile strength but corrodes , used as structural materials

stainless steel (alloy)

• iron + carbon + other elements (nickel/chromium — discourage corrosion)

• widely used in domestic and industrial appliances due to strength and corrosion resistance

bronze alloy

• copper+ tin

• coins , medals ,tools

ionic compounds have

giant ionic lattice structure with strong ionic bonds

• metal x non metal

ionic bonding

electrostatic forces of attraction between oppositely charged ions in an ionic lattice

lewis structure

1. use valence electrons (latest shell)

strength of ionic bond is determined by

1. charge on the cation and charge on the anion (higher = stronger)

   1. if same anion ignore it and compare cation charge

2. radius of the cation and radius of the anion (smaller=stronger)

charge x charge / sum of ionic radius

MgO vs CaO , which has higher MP

• both have the same anion

• charge of Mg and Ca are the same

• Radius of Ca is larger than Mg

• MgO has stronger ionic bonding + more energy needed to over stronger electrostatic forces of attraction/ionic bonds

• MgO has higher MP

physical properties of ionic compounds

1. good electrical conductivity in molten/aq state

2. brittle

3. high MP

ionic compound —good electrical conductivity in molten/aq state

ions are mobile , can move in response to applied voltage

• application : electrolytes

ionic compound—brittle

movement of ions within the lattice places ions of the same charge alongside each other , repulsive forces causes it to split (because when pushed together cation may bump into cation)

• application : electric wires and cables

ionic compound —high MP

alot of energy is needed to overcome the strong ionic bonds

• application : MgO is used to Lin the walls of blast furnace (?)

covalent bonding

electrostatic forces of attraction between 2 nuclei of non metals and the shared pair of electrons

covalent bonds are formed when

non metal atoms share valence electrons to achieve noble gas configuration

single bond/double bond/triple bond

sharing of __ pair of electrons between atoms

strength of covalent bond is

• proportional to the number of bonds between atoms (triple=strongest)

• inversely proportional to bond length (longer bond length , weaker bond)

VSEPR theory ( valence shell electron pair repulsion)

electron domains are placed as far apart as possible in space to minimise repulsion

• allow the shape of the molecule to be determined by repulsion between electron domains

the electron domain geometry is determined by the

total number of electron domains found the central atom

• spatial arrangement of all the electron domains

molecular geometry of molecule is determined by

number of bonding electron domains (bond pair) and number of non bonding electron domains (lone pair) around the central atom

when number of electron domain =2 , Eg: CO₂

1. electron domain geometry : linear

2. number of bonding electron domains : 2

3. number of non-bonding electron domain : 0

4. molecular shape : linear (180)

when number of electron domain =3 , Eg: BF₃

1. electron domain geometry : trigonal planar

2. number of bonding electron domains : 3

3. number of non-bonding electron domain : 0

4. molecular shape : trigonal planar (120)

when number of electron domain = 3 , Eg: SO₂

1. electron domain geometry : trigonal planar

2. number of bonding electron domains : 2

3. number of non-bonding electron domain : 1

4. molecular shape : V shaped (117)

when number of electron domain =4 , Eg : CH₄

1. electron domain geometry : tetrahedral

2. number of bonding electron domains : 4

3. number of non-bonding electron domain : 0

4. molecular shape : tetrahedral (109.5)

when number of electron domain =4, Eg:NH₃

1. electron domain geometry : tetrahedral

2. number of bonding electron domains : 3

3. number of non-bonding electron domain : 1

4. molecular shape : trigonal pyramidal (107)

when number of electron domain =4 , Eg: H₂O

1. electron domain geometry : tetrahedral

2. number of bonding electron domains : 2

3. number of non-bonding electron domain : 2

4. molecular shape : V shaped (105)

giant covalent structure / macromolecular structure

atoms linked together by covalent bonds to form a lattice structure

allotropes

different forms of an element in the same physical state

graphite structure (allotrope)

Each C atom is covalently bonded to 3 other C atoms , forming hexagons in parallel layers with bond angles of 120

The layers are held by weak van Der waals’ forces of attraction and can slide over each other

graphite electrical conductivity

• good conductor of electricity

• each C contains one non bonded electron which is delocalised along the parallel layers

graphite appearance + special properties + uses

appearance : non lustrous , grey crystalline solid

special properties : soft and slippery, brittle , high MP

uses : dry lubricant , in pencil , electrode rod in electrolysis

diamond (allotrope) structure

Each C atom is covalently bonded to 4 other tetrahedrally arranged in a regular repetitive pattern with bond angles of 109.5

diamond electrical conductivity

non conductor of electricity . All valence electrons of C are involved in covalent bond formation

diamond appearance + special properties + uses

appearance : highly transparent , crystalline solid

special properties : cannot be scratched , brittle , high MP

uses: jewellery , tools and machinery for cutting glass

simple covalent structure

covalent bonds hold atoms together in a molecule while intermolecular forces of attraction hold molecules together

• non metal x non metal

strength of intermolecular forces determines the

physical properties of a substance — MP and BP

intermolecular forces include

1. van der Waals forces

2. hydrogen bonding

Properties of simple covalent molecules

1. no electrical conductivity — no delocalised electrons/mobile ions

2. low MP and BP — little energy needed to overcome weak intermolecular forces of attraction

van der Waals forces strength is determined by

number of electrons in the molecule (greater=stronger, as more energy is required to overcome…)

which has higher MP , CH₄ or C₂H₆

*count the MR of each first , MR is proportional to electrons

• C₂H₆ has higher Mr

• More electrons

• strength of van Der Waals forces of attraction is higher , more energy needed to overcome

• MP increases

electronegativity

measure of the ability of its atoms to attract electrons in a covalent bonding

electronegative atom

when a molecule contains hydrogen and is covalently bonded to

1. fluorine

2. oxygen

3. nitrogen

• they are attracted to each other by hydrogen bond

hydrogen bond

strongest form of intermolecular forces of attraction

• BP of molecules forming hydrogen bonds are higher

• stronger than van Der Waals

CH₄ vs H₂O , which has higher MP

• both have simple covalent structure

• H₂O has hydrogen bonded to very electronegative O atom and can form stronger hydrogen bonds between molecules

• CH₄ forms weak van Der Waals forces between molecules

• more energy needed to overcome stronger hydrogen bonds

• H₂O higher MP