Chem

Electrons : Negatively charged particles

Isotope : Atoms that contain the same number of protons, but different number if neutrons

Ion : When an atom gains or loses one or more electrons

Covalent bonding : A shared pair of electrons (occurs between non-metals)

Molecule : Two or more atoms covalently bonding together

Diatomic : Two atoms covalently bonded together (e.g. O2, N2, Cl2)

Atoms

  • The building blocks of matter

  • An atom is made of a central nucleus, containing positively charged protons and neutrally charged neutrons

  • Negatively charged electrons spin around the nucleus in shells

  • Protons and Neutrons are collectively called Nucleons

Diagram of an atom

  • Atoms are neutrally charged - equal number of protons and electrons

  • Most of an atoms mass is concentrated in the nucleus

  • Protons, electrons and neutrons are known as subatomic particles

Atomic Number and Mass Number

  • Atomic Number - Number of protons OR number of electrons

  • Mass Number - Number of protons + number of neutrons

Isotopic Symbol

Elements and Isotopes

  • Element - An element is made up only one kind of atom (Eg - Hydrogen, Carbon, Oxygen)

  • Isotopes - Atoms of the same element with different numbers of neutrons

Lets consider Carbon -

Carbon has an atomic number of 6.

It has 3 isotopes with mass numbers 12, 13 and 14

Ions

  • Ions are formed when an atom loses or gains electron(s)

Atoms lose an electron (positive ions) = CATION

Atoms gain an electron (negative ions) = ANION

  • An ion is a charged particle because it contains an unequal number of protons and electrons

  • An atom which is charged is considered to be ionised

  • The charge of an ion is equal to the number of electrons lost or gained

Lets consider Sodium (Atomic no. = 11, Mass no. = 23)

A sodium atom (e=11, p=11, n=12) > Na

If it loses an electron (e=10, p=11, n=12) > Na+ (Cation)

Electron configuration

  • Shows how many electrons are in each shell

  • The outer most shell is called the Valence Shell

Note: For year 10, follow the rule 2,8,8,2 for the first 20 elements

Emission spectra and electron shells

  • When atoms are heated in a flame, the electrons gain energy and become excited

  • With this extra energy, they are able to jump from their electron shell to the next outer shell

  • When they return to their original shell, the energy is lost in the form of light. This light can vary in color depending on the atom

  • Each atom has its own distinct ray of colors

Non polar vs polar

Non polar

  • Molecules that contain only one type of element (H2, N2, O2, F2, etc.)

  • Hydrocarbons (CH4, C2H6, C3H8, etc.)

  • When a molecule is geometrically symmetrical

  • Difference in electronegativities is less than 0.5

Polar

  • When a molecule is geometrically asymmetrical

  • Atoms with different electronegativities

  • Difference in electronegativities is more than 0.5

Bonding

  • Most atoms join with other atoms to form small groupings called molecules OR large, regular arrangements called lattices

  • The link between these atoms are called chemical bonds

  • Group 18 elements (The nobles gases), tend not to bond. They exist as single atoms and are referred to as Monatomic

There are 3 types of bonding:

Ionic: Occurs between metal atoms and non-metal atoms

Covalent: Occurs between non-metal atoms

Metallic: Occurs between metal atoms

Ionic bonding

The transfer of electron(s) from one atom to another. This results in the formation of cations and anions which are held together by a strong electrostatic force of attraction. (i.e. +ve charged particles are attracted to -ve charged particles)

Cations: Metallic ions

Metals which have lost electrons and have an overall +ve charge

Anions: Non-metallic ions

Non-metals which have gained electrons to become -ve charged

Metallic Bonding

Arrangement of Atoms in Metals

  • In metals, the atoms are packed closely together

  • When these atoms get very close to each other, the valence electrons merge into a cloud charge moving continuously throughout the structure

  • A network of positive ions results from metal atoms ‘losing’ their valence electrons and these electrons form a sea of delocalised negative charge

  • The cations stay in fixed positions in the metal lattice, and can only vibrate (they do not move)

  • Only the outer (valence) electrons are free to move

It is the electrostatic attraction between the network of cations and the delocalised valence electrons that holds the atoms together. This attraction is called metallic bonding.

Properties of Metallic Substances

Good conductors of electricity

  • When an electric field is applied, one end of the metal becomes positive and the other negative

  • The delocalised electrons move to the positive end to complete the circuit

  • This causes an electric current and electricity to be conducted

  • In other words, these outer shell electrons can respond to an applied electric field thereby completing the circuit

Good conductors of heat

  • The delocalised electrons are able to absorb heat from the surroundings

  • They move faster and bump into each other and the cations in the lattice

  • This causes heat to be transferred down the piece of metal

High Melting and Boiling Points

  • There is strong electrostatic attraction between the delocalised electrons and network of positive cations

  • A larger amount of thermal energy is required to break this attraction

Lustre

  • Metals are lustrous as the delocalised electrons are able to reflect UV light

Malleability

  • When a force is applied, the layers of cations are able to slide past each other

  • The metallic bond doesn’t break due to the non-directional electrostatic attraction between the positive cations and negative delocalised electrons

  • The rows of cations in the lattice are pushed closer together

  • This means that metals can be bent (or hammered) and pulled into wires without breaking

High density

  • The cations are tightly packed together in the lattice structure

Properties of Ionic Compounds

High Melting and Boiling Points

  • There is strong electrostatic attraction between the positive cations and negative anions

  • Large amounts of thermal energy are required to break this attraction and separate the ions

Hard

  • The cations and anions are held together are held together by strong electrostatic attraction

  • They are strongly attracted to each other and are difficult to separate

Solid state cannot conduct electricity

  • The cations and anions are arranged in a fixed lattice

  • The ions are unable to move to complete the circuit

Molten state can conduct electricity

  • The cations and anions are free to move past each other as heat breaks the lattice

  • Ions are able to move towards opposite ends of the electric field and complete the circuit by forming an electric current

Aqueous state can conduct electricity

  • The cations and anions are free to move past each other as the water molecules break the lattice

  • The ions are able to move towards opposite ends of the electric field and complete the circuit by forming an electric current

Brittle

  • When a force is applied, the layers of ions move past each other and the like charges align

  • This causes them to repel (like charges repel, opposite charges attract) and the lattice shatters

Usually soluble in water

  • Water molecules are able to move between the ions

  • This causes the ions to be able to move freely from the lattice