Chemistry Definitions 10/02/2014
Element
an element cannot be broken into anything simpler
Atom
the smallest part of an element
Molecule
group of atoms combined (bonded, joined together)
Law of Conservation of Matter
Matter is neither created or destroyed in the course of a chemical reaction
Atomic Number
Number of protons in the nucleus of an atom of the element
Mass Number
The sum of the number of protons and the number of neutrons in the nucleus
Relative Atomic Mass
average mass of atom(s) of element relative to 1/12 mass of carbon–12 atom
Isotopes
Atoms of same element having different mass numbers
Principle of Operation Mass Spectrometer
Positively charged ions are separated on the basis of their relative mass in a magnetic field
Processes Involved in Mass Spectrometer
Vaporisation, Ionisation, Acceleration, Separation, Detection- of sample
Radioactivity
Spontaneous random emission of radiation from unstable nuclei due to decay of a nucleus
Alpha Particles
Are helium nuclei emitted from the nucleus of radioactive isotopes
Beta Particles
Are electrons emitted from the nucleus of radioactive isotopes
Gamma Rays
Are high energy electromagnetic radiation emitted from the nucleus of radioactive isotopes
Radioisotopes
Isotope with unstable nucleus
Half Life
Time taken for half of the radioactive isotopes in a sample to decay
Energy Level
Energy of an electron in orbit around nucleus
Sub-Level
An atomic sub-level is a sub-division of a main energy level consisting of one or more orbitals of the same
energy
Line Spectrum
Is a series of coloured lines against a dark background
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Chemistry Definitions 10/02/2014
Absorption Spectrum
Is the spectrum observed after light has been passed through the element
Ground State
Electron is in lowest energy state
Excited State
Electron is in higher energy state than lowest energy state
Bohr’s Atomic Theory
The electron is restricted to fixed energy levels.
Electrons occupy the lowest available energy level.
Electrons can move to a higher energy level if it receives a certain amount of energy.
This energy absorbed must equal exactly the energy difference between the ground state and excited state {(E2 –
E1), E2 = excited state, E1 = ground state}
The electron is unstable in the excited state and drops back to a lower energy level emitting light of a definite
frequency (f)
(E2 – E1 = hf)
Uncertainty Principle
not possible to measure the exact position and momentum (velocity) of electron in an atom
simultaneously
Atomic Orbital
region around the nucleus of an atom where there is a 99% probability of finding an electron
Atomic Radius
Half distance between the centres of the atoms in a single homonuclear bond (of singly-bonded atoms of the
same element)
First Energy of Ionisation
Minimum energy to remove most loosely-bound electron from an isolated atom in its ground state
Electronegativity
Relative attraction an atom of an element has for a pair of electrons in a covalent bond
Oxidation
Loss of electrons
Reduction
Gain of electrons
Oxidising Reagent
Is a substance that allows oxidation to happen by gaining electrons itself
Reducing Reagent
Is a substance that allows reduction to happen by losing electrons itself
Electrolysis
Production of chemical change when electricity passes through an electrolyte
Electrolyte
Is a substance that conducts electricity when dissolved in water or when molten
Valency
Is the number of bonds an atom of the element forms when it reacts
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Chemistry Definitions 10/02/2014
Ionic Bonding
Bond involving transfer (loss and gain) of electrons
Covalent Bonding
Bond involving sharing of electrons
Polar Covalent Bonding
Type of bonding with unequal sharing of bonding electrons
Intramolecular Bonding
Forces between atoms in molecules
Intermolecular Bonding
Attractive forces between molecules
Hydrogen Bonds
Intermolecular attraction involving slightly positive hydrogen atom and highly electronegative
element/atom, (F, O, N)
Diffusion
Is the spreading and mixing of substances due to random motion of their particles
Boyle’s Law
The volume of a fixed mass of gas is inversely proportional to its pressure at a constant temperature
Charles’ Law
volume varies directly with kelvin (absolute) temperature for a definite mass of gas at constant
pressure
Avogadro’s Law
Equal volumes of gases contain equal numbers of particles {moles, molecules, atoms (for noble gases)} under
same conditions (temp. and pressure)
Gay Lussac’s Law of Combining Volumes
The volumes, measured at the same temperature and pressure, of reacting gases and their gaseous
products are in small whole number ratios
The Mole
Amount of a substance containing as many particles as the number of atoms in (12 g) of carbon-12
or amount of a substance equal to the relative formula (molecular) mass expressed in grams
or amount of a substance containing the Avogadro number (Avogadro constant, L, 6 × 1023) of
particles
Relative molecular mass
Of a substance is the average mass of a molecule relative to 1/12 of the mass of an atom of carbon-12
Molar Mass
Of a substance is the mass in gams of a mole of the substance
Ideal Gas
A gas that obeys the gas laws at all values of temperature and pressure or “A gas that obeys the
assumptions of the kinetic theory”
Empirical Formula
Shows the simplest ratio of atoms in a molecule
Molecular Formula
Of a compound indicates the actual number of atoms of each element present in a molecule
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Chemistry Definitions 10/02/2014
Structural Formula
Of a compound indicates the arrangement of atoms within a molecule of the compound
Activation Energy
Minimum energy required for particles colliding to react
Effective Collision
Results in reaction between colliding particles (molecules)
Instantaneous Rate
Of a reaction is the rate at a particular point during the reaction
Heterogeneous Catalysis
reactant(s) and catalyst in different phase(s)
Rate Of Chemical Reaction
change of concentration
time
Catalyst
Substance that alters (speeds up) rate of reaction which is chemically unchanged at the end
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