UNIT 1 DFINITIONS- ALL THE DEFINITIONS YOU NEED TO KNOW WITH EXAMPLES!!

Hi all!! Today I am coming with a different post for you. Here you have all the definitions you might be interested in for your Unit 1 Chemistry AS-level. If I missed any, please let me know and I'll add them to the list. However, I believe that if you know all the ones that are already here, you are good to go. Also, I included some examples in many of the definitions for you to visualise my point. Without further ado, let's get started.

I invite you to my youtube channel for more practise questions on every single topic. You can also find two Unit 1 past papers (2018 and 2019) there with a full explanation of every single question.

Definitions:

1.1

Oxidation number- number of electrons that need to be added or taken away from an element to make it neutral.

1.2

Atomic mass (Z)- number of protons in nucleus of an atom.

Mass number (A) – number of protons and neutrons added together in nucleus of an atom.

Isotope- atoms that have the same number of protons but different number on neutrons.

e.g. C-12 and C-14, they both have the same number of protons (atomic number) but their mass number changes, so they have a different number of neutrons.

Ion- when the number of electrons and the number of protons in an atom does not equal.

e.g. Sodium, Na has 11 electrons and 11 protons, when it becomes an ion, Na+ (for examle by ionic bonding) it has 11 protons but 10 electrons because 1 electron is lost (donated).

Alpha particle- it is the Helium nucleus, 2 protons and 2 neutrons (positive charge).

Beta particle- fast moving electron (negative charge).

Gamma particle- electromagnetic wave (no charge).

Half-life – time taken for half of the radioactive species to decay.

Atomic orbital- region in an atom in which can hold up to two electrons with opposite spins (this is one box when we draw electronic configurations).

Electronic configuration- arrangement of electrons in an atom.

Shielding – repulsion of electrons in different shells (electrons in inner shell will repel the electrons in the outer shell).

Molar first ionisation energy – energy needed to remove one mole of electrons from one mole of its gaseous atom.

Successive ionisation energy- energy needed to remove electron from an atom (many successive ionisation energies until you have no more electrons in an atom).

1.3

Relative atomic mass (Ar)- average mass of one atom relative to 1/12th the mass of one atom of carbon-12.

Relative isotopic mass- mass of an isotope relative to 1/12th the mass of an atom of carbon-12.

Relative formula mass (Mr)- average mass of a molecule relative to 1/12th the mass of an atom of carbon-12.

(This means that you use the mass number that is stated on the periodic table. All of these numbers are relative to 1/12th the mass of one atom of carbon-12. The definition may seem a little bit tricky but it isn't and if you can see all three definitions look nearly the same).

One mole- amount of any substance that contains the same number or particles as there are atoms in exactly 12g of carbon-12.

Molar mass- mass of one mole of a substance.

Empirical formula- simplest formula with the simplest whole number ration.

Molecular formula- formula with the actual number of atoms ( it is the empirical formula or a multiple of empirical formula).

Molar volume- it is the volume per mole of gas.

Atom economy – mass of required product (Ar)/ total mass of reactants (Mr) x100%

%yield – mass of product obtained/ theoretical mass x 100%

1.4

Ionic bond- bond formed by the attraction between positive and negative ions.

Covalent bond- bond where a pair of electrons is shared between two atoms (with opposite spins).

In your exam, you can only put the outer shell.

Coordinate bond- it is a covalent bond but both of the shared electrons come from the same atom.

Both of the electrons come from nitrogen.

Metallic bonding- two (or more) metals donate their outer electrons to a sea of delocalised electrons. The bond is formed between the positive nucleus of the atom and negative sea of electrons.

Electronegativity – shows how easy it is for an atom to attract electrons (electron-attracting power). If in a compound one atom is more electronegative than the other it will attract electrons to itself more and we call them 'slightly negative' and 'slightly positive' atoms.

e.g. between H and Cl. Cl is more electronegative.

The most electronegative atom is fluorine.

Intermolecular bonding- weak bonding that holds the molecules together

e.g. Van der Waals, hydrogen bonding;

Intramolecular bonding – this is the strong bonding within the molecule between atoms

e.g. ionic, covalent, coordinate, metallic;

Van der Waals- combine two types of intermolecular forces: dipole-dipole and induced dipole- induced dipole.

Dipole-dipole – strong forces (attractive) between positive end of one molecule and negative end of another molecule.

Induced dipole- induced dipole – weak forces (attractive) between a polar molecule which induces an atom (non-polar) and disturbs its arrangement of electrons.

1.5

Co-ordination number – the number of atoms or ions which immediately surround a central atom (in a crystal or complex).

1.6

Redox- oxidation and reduction which happens during one process (Oxidation –loss of electrons OIL, Reduction – gain of electrons).

1.7

A reversible reaction- reaction that can go either forward or reverse depending on the conditions.

Dynamic equilibrium – when the forward and reverse reactions occur at the same rate.

Position of equilibrium- position in a reaction (either more to the products or reactants) where equilibrium (balance between products and reactants) is present.

Le Chatelier’s principle – if the position of equilibrium is subjected to a change, equilibrium will shift to minimise that change.

Acid- is a proton (H+) donor.

Base- is a proton (H+) acceptor.

Strong acid- fully dissociates (fully splits into ion) in aqueous solution.

Weak acid- partially dissociates (partially splits into ions) in aqueous solution.

Concentrated acid- large quantity of acid and a small quantity of water.

Dilute acid- small quantity of acid and a large quantity of water.

Salt- compound formed when a metal ion replaces hydrogen ion in an acid.

e.g. hydrogen in the acid is replaced by a metal ion, in this example sodium.

Standard solution – solution of which we know the concentration accurately.

PS. Please remember, I am only a student, and as anyone, I can make mistakes. If you think you can see one, don't hesitate and comment (either here on on my youtube channel) Thank you!