CHEM - 7 metallic bonding

what is a metallic bond?

a strong electrostatic attraction between positive metal ions and delocalised electrons

why do metal conduct electricity

because the delocalised electrons are free to move and carry charge when a voltage is applied

why are metals malleable and ductile

Because the layers of metal ions can slide over other easily

what is the structure of a metal

a regular lattice of positive metal ions surrounded by a sea of delocalised electrons

why do metals have a high melting point and boiling point

due to strong electrostatic forces between metal ions and delocalised electrons that require a lot of heat energy to break

what is the general equation for metal reacting with water

metal + water → metal hydroxide + hydrogen

what are the products of potassium reacting with water

potassium hydroxide + hydrogen

why does magnesium react with steam but not cold water

because steam provides more energy, allowing the reaction to occur

what is the reactivity series from most reactive to least

potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold

what does a more reactive metal do in a displacement reaction

it displaces a less reactive metal from its compound

what is oxidation in terms of oxygen and electrons

gain of oxygen or loss of electrons

what is reduction in terms of oxygen and electrons

loss of oxygen or gain of electrons

what is meant by redox reaction

a reaction where both oxidation and reduction occur

what is reducing agent

a substance that donates electrons ( causes another species to be reduced) itself oxidised

what is an oxidising agent

a substance that accepts electrons ( causes another species to be oxidised) itself reduced.

what is the word equation for iron rusting

water + iron + oxygen → hydrated iron(|||) oxide (rust)

why is aluminium resistant to water and steam despite being reactive

It forms a protective oxide layer that prevents further reaction

name 3 methods to prevent rusting

Barrier methods (e.g. painting), galvanising and sacrificial protection

why is thermite reaction useful in rail repairs

it produces molten iron through an exothermic reaction that can weld tracks

what conditions are necessary for the rusting of iron

oxygen + water

barrier method 

• painting, greasing, oiling

• creates a physical barrier

• stops oxygen and water from reaching iron

galvanising

• a zinc coating is applied

• this cause ZnO to be formed on the outside

• This acts as a physical barrier

• if the metal is scratched it fills the gap by forming ZnO

Sacrificial Protection

• The More reactive metal is attached ( to the iron )

• then this metal oxidises

• the electrons released prevent iron from being oxidised itself

What is an alloy and 2 examples

A mixture of 2 or more metals or a metal with a non-metal such as carbon

• steel is an alloy, made from Iron and Carbon

• brass is an alloy, 70% copper and 30% zinc

Metallic bonding

It is an electrostatic attraction between a positively charged ion and its delocalised electrons.

Delocalised

free to move throughout the whole structure

why do metals have high mpt/bpt

???

metallic bonds are very strong meaning a large amount of heat energy is needed to break the bond causing high mpt/bpt

why are metals ductile/ malleable

• The ions are arranged in layers

• these layers can slide over one another

• this allows the metal to be bent or shaped 

why are alloys harder than metals

• the metal ions are different sizes

• this disrupts the lattice structure

• layers of ions cant slide over one another

why are they good conductors of electricity

the delocalised electrons in the metals can carry electrical charge throughout the metal

why are metals good conductors of thermal energy

the delocalised electrons can transfer heat throughout the structure.

name the top five metals on the reactivity scale

• potassium

• sodium

• lithium 

• calcium

• aluminium

name the bottom 5 metals in the reactivity series

• iron

• hydrogen

• copper

• silver

• gold

oxidation

the loss of electrons

reduction

the gain of electrons

redox

oxidation reactions and reduction reactions always happen together, and together are know as redox reactions

oxidising agent

causes another species to be oxidised, itself reduced

reducing agent

causes another species to be reduced, itself oxidised

what means a metal has a stronger metallic bond

• higher charge on the metal

• smaller ion ( protons positive charge is pulling the negative electrons closer since it has less electrons but same strength)

state 3 physical properties of metal

• hard

• malleable

• high mpt/bpt

• conductors

• strong

• ductile

displacement

when a more reactive metal displaces a less reactive metal from its aqueous solution.