Year 10 GCSE Chemistry - C2.1 Bonding

What electrons do

Orbit the nucleus in shells

First shell holds a maximum of -

2 electrons

Second shell holds a maximum of -

8 electrons

Third shell holds a maximum of -

8 electrons

What the group # shows (periodic table)

# outer electrons

What the period # shows (periodic table)

# electron shells

Properties of noble gases

Inert and stable

Ion

Electrically charged particle formed when an atom, or group of atoms, loses or gains electrons

Metal atoms do what to form + ions

Lose electrons

Non-metal atoms do what to form - ions

Gain electrons

What stay constant when an atom forms an ion

# protons and neutrons

What you need to work out an ion's electronic structure

Electronic structure of the original ion, and the # electrons it lost or gained

Electronic structure of a sodium atom

2.8.1

Stable atoms or ions have -

Full outer shells

Electron diagram

Represents the electronic structure of an atom or ion

How you draw an electron diagram

A circle to represent each shell, and dots or crosses to represent its electrons. Ions go inside brackets with the change written at the top right. The element's symbol potentially written at the centres instead of showing a nucleus. Have a go at a few

Dot-and-cross diagrams

Use of both dots and crosses allow you to see which atoms provided particular electrons

What dot-and-cross diagrams can be used to show

Covalent bonds

What happens when a metal and non-metal react

Electrons are transferred from the metal atoms to non-metal atoms so both achieve more stable electronic structures

What ionic compounds contain in their solid state

Positive and negative ions arranged in a regular way, called a giant ionic lattice

Ionic bonds

Strong, electrostatic forces of attraction between metal and non-metal atoms, holding oppositely-charged ions in place, acting in all directions

Space-filling model

Way of representing ionic compounds

Binary ionic compound

Composed of two elements (a single metal e.g. sodium and non-metal e.g. chlorine)

Giant ionic lattice

Exists in three dimensions, but you can only draw it in two dimensions

What balls and sticks represent in a ball-and-stick model

Balls represent ions and plastic links represent an ionic bonds

Positive things about ball-and-stick models

Give you a clearer idea of the structure and shape of the lattice

Limitations of ball-and-stick models

Ions should be close together - bonds are forces rather than physical objects made from matter

What you can write before brackets in ions notation

Coefficient

What we need to know to find formulae of ionic compounds

Charges of ions

How we can find charges of ions

Periodic table

Transition metals form -

More than one ion

Positive (group) ions

Ammonium, NH4+

Negative (group) ions

Hydroxide, OH -, nitrate, NO3 -, sulfate, SO4 2- and carbonate, CO3 2-

Covalent bond

Shared pair of electrons, forming between two non-metal atoms when they get close enough to share atoms in their outer shells. They therefore complete their outer shells

What each pair of electrons in the intersection of overlapping circles of a dot-and-cross diagram represents

A covalent bond

When drawing a dot-and-cross diagram for covalent bonds, only the what are shown?

Outer shells

Stick notation

Each line between symbols represents a bond. You can have multiple lines to represent multiple e.g. double bonds

Molecule

Particle in which non-metal atoms are joined to each other by covalent bonds

Simple molecule

Only contains a few atoms

Examples of simple molecules

Hydrogen, oxygen, water and carbon dioxide

Covalent bonds between atoms in a simple molecule are -

Strong

Intermolecular forces in a simple molecule are -

Weak

Intermolecular forces

Between molecules

Limitations of ball-and-stick models (for simple molecules)

Sizes of atoms and lengths of bonds are exaggerated, and it suggests that electrons that make bonds do not move

Displayed formula

Drawn for simple molecules, where each atom is represented by its chemical symbol and each covalent bond is a straight line

Limitations of a displayed formula

Does not show three-dimensional shape of molecule

Space-filling models

Way of representing molecules, using interconnected spheres to show electron clouds of atoms connecting together

Giant covalent structures / lattices

Have a repeating lattice. Composed of very many non-metal atoms covalently bonded, arranged in a repeating, regular pattern called a giant lattice

Allotropes

Different forms of the same element in same physical state, having different molecular structures

Two examples of minerals that are allotropes of carbon

Diamond and graphite

What explains the differences between diamond and graphite

Arrangement of atoms

Empirical formula

Shows simplest whole-number ratio of elements in a compound

Empirical formula for diamond

C

Properties of diamond

Strong and hard, crystalline and high melting and boiling points

Crystalline

Solid made up of crystals in which particles are arranged in a regular, repeating pattern

Why diamond is crystalline

Each carbon atoms is covalently bonded to four other carbon atoms

Structure of graphite

Each carbon atom is bonded to three others, its fourth unshared electron is delocalised. Has layers of covalently bonded carbon hexagon rings, although no covalent bonds between layers so can 'slide'

Properties of graphite

Soft and slippery, conducts electricity (delocalised electrons) and high melting and boiling points

Buckminster fullerene aka

Bucky ball

Properties of Buckminster fullerene

Cannot conduct electricity or heat

Structure of Buckminster fullerene

Allotrope of carbon with simple molecular structure, and so chemical formula C60

Fullerenes

Form of carbon having a large spheroidal molecule consisting of a hollow cage of sixty or more atoms, of which buckminsterfullerene was the first known example

What simple molecular substances are made of

Molecules

Properties of simple molecular substances

Low melting and boiling parts, as there are weak forces between molecules. Do not conduct electricity because molecules are not electrically charged - they are insulators

What atoms are held together by in covalent bonds

Shared electrons

State of metals, apart from mercury, at room temperature

Solid

Structure of metals

Atoms packed together in a regular way forming a giant metallic lattice

How a giant metallic lattice can be modelled

Drawing circles or spheres arranged in a regular pattern, in contact with each other

Properties of metals (remember, they link to structure!)

Conduct electricity, high melting and boiling points, shiny, malleable and ductile

Leading up to / formation of metallic bonds

Electrons leave outer shells of metal atoms forming s 'sea' of delocalised electrons around positively charged metal ions

Delocalised electrons

Free to move through the structure of a metal

Metallic bonds

Strong electrostatic forces of attraction between delocalised electrons and closely packed, positively charged metal ions

Models of metals

As a metallic structure extends in three dimensions, and its metallic bonding also extends in three dimensions, you lose some information when representing structure and bonding in two dimensions

Polymer (molecule)

Made from many smaller monomer molecules

Monomer

Simple molecule consisting of covalently-bonded, non-metal atoms, able to join end to end in chemical reactions to produces longer polymer molecules

Example of artificial polymers

Plastics such as nylon

Example of natural polymers in the body

Complex carbohydrates, DNA and proteins in skin

Many ethene molecules make

Polyethene / polythene

Many amino acids make

Protein e.g. keratin in hair

Simple model showing how polymers form

Squares or circles (representing monomers) might be joined up with a line to show a polymer

Three ways of modelling monomers

Dot-and-cross diagrams, space-filling models and ball-and-stick models

What is much more difficult for polymer molecules than monomers

Modelling them

Space-filling model DNA, reiterating difficulty of modelling polymers

Starch

Complex carbohydrate

'Wavy-line' diagram for modelling polymers

Each polymer molecule is drawn as a wavy line, sometimes with straight lines in between them to represent covalent bonds between individual polymer molecules. Weak intermolecular forces between polymer molecules are not shown

Two examples of polymers made from several different types of monomers

Proteins and DNA

Example of polymer made from one type of monomer

Polythene

Formula for ethene

C2H4

What idea poly(ethene) can be modelled using

Repeating unit

Repeating unit

Section of polymer repeated over and over again

Ionic bonding

Between metals and non-metals, where electron

Description of ionic bonding

Electrons are transferred from metal to non-metal atom. Results in giant ionic lattice

Properties of giant ionic lattices

Hard, crystalline, soluble in water and do not conduct when solid although do conduct when liquid or dissolved

What is required for a substance to conduct electricity

Charged particle free to move around

Why a metal can conduct electricity

Delocalised electrons are always free to move around

Why ionic compounds in their solid state cannot conduct electricity

Oppositely charged ions are fixed into place, unable to move around and carry a charge

Why ionic compounds dissolved in water can conduct electricity

Ions aren't held together by strong electrostatic forces of attraction anymore, therefore free to move around and conduct electricity