National 5 Chemistry Summary Notes: Chemical Changes and Structure

Vocabulary practice flashcards covering Unit One: Chemical Changes and Structure for National 5 Chemistry, including Rates of Reaction, Atomic Structure and the Periodic Table, Chemical Bonding and Structure, Chemical Formulae, and Mole Calculations.

Exothermic Reaction

A chemical reaction that releases heat energy to the surroundings, causing the temperature of the surroundings to increase.

Endothermic Reaction

A chemical reaction that absorbs energy/heat from the surroundings, causing the temperature of the surroundings to decrease.

Test for Carbon Dioxide

A gas identification test where the gas is bubbled through limewater, turning the lime water milky (cloudy).

Test for Oxygen

A gas identification test where the gas relights a glowing splint.

Test for Hydrogen

A gas identification test where the gas burns with a "pop".

Catalyst

A substance that speeds up a chemical reaction by providing an "easy route" from reactants to products, but is not used up and can be recovered chemically unchanged with unchanged mass at the end of the reaction.

Enzymes

Biological catalysts found in living things that speed up chemical reactions, allowing them to occur faster at lower temperatures.

Average Rate of Reaction

The measured change in a property (such as mass or volume) divided by the time taken for that change to occur: $\text{Average rate} = \frac{\text{measured change}}{\text{time taken}}$.

Proton

A sub-atomic particle found in the nucleus of an atom with a charge of $+1$ and a mass of $1\,\text{amu}$.

Neutron

A neutral sub-atomic particle found in the nucleus of an atom with a charge of $0$ and a mass of $1\,\text{amu}$.

Electron

A sub-atomic particle that orbits outside the nucleus in energy levels (shells), carrying a charge of $-1$ and an approximate mass of $0\,\text{amu}$.

Atomic Number

The number of protons in the nucleus of an atom, which determines the order of elements in the Periodic Table.

Mass Number

The total number of protons plus the number of neutrons in an atom's nucleus ($\text{Mass number} = \text{protons} + \text{neutrons}$).

Isotopes

Atoms of the same element that have the same atomic number (number of protons) but different mass numbers due to differing numbers of neutrons.

Relative Atomic Mass

The average mass of the mass numbers in a natural sample of an element, taking into account all of its isotopes and their relative abundances.

Alkali Metals

The very reactive elements found in Group 1 of the Periodic Table, such as lithium and sodium, having one electron in their outer shell.

Halogens

The very reactive non-metal elements found in Group 7 of the Periodic Table, such as fluorine and chlorine, having seven electrons in their outer shell.

Noble Gases

The completely unreactive elements found in Group 8 (or 0) of the Periodic Table, possessing full outer electron shells.

Covalent Bond

A bond formed when two non-metal atoms share a pair of electrons, held together by the common electrostatic attraction of the two positive nuclei for the shared pair of negative electrons.

Molecule

A group of atoms held together by covalent bonds.

Diatomic Molecule

A molecule composed of only two atoms bonded together, such as the diatomic elements ($H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, $I_2$) or compounds like $HCl$ and $CO$.

Covalent Molecular Substance

A substance composed of discrete molecules held together by weak intermolecular forces, which break upon melting or boiling, resulting in low melting and boiling points.

Covalent Network

A giant lattice structure composed entirely of atoms joined by strong covalent bonds (e.g., diamond, graphite, silicon, boron, silicon dioxide), requiring significant energy to melt and resulting in very high melting points.

Ionic Bond

The electrostatic force of attraction between oppositely charged ions (positively charged metal ions and negatively charged non-metal ions).

Ionic Lattice

A regular, repeating three-dimensional arrangement of alternating positive and negative ions held together by ionic bonds.

Electrolyte

A molten ionic compound or aqueous ionic solution that conducts electricity due to free-moving ions.

Electrolysis

The decomposition and breakdown of an ionic compound into its elements using an electric current from a direct current ($\text{d.c.}$) power supply.

Valency

The combining power of an element, directly related to its group number in the Periodic Table and the number of bonds an atom of that element can make.

Group Ions

Charged particles containing two or more chemically combined atoms of different elements that stay together during chemical reactions (e.g., $SO_4^{2-}$, $OH^-$, $CO_3^{2-}$, $NH_4^+$).

Ionic Formula

A chemical formula that explicitly shows the symbols and charges of each ion present, arranged such that the overall combined electric charge is zero.

State Symbols

Letters written in brackets after chemical formulae in equations to indicate physical state: $(s)$ for solid, $(l)$ for liquid, $(g)$ for gas, and $(aq)$ for aqueous solution.

Gram Formula Mass (GFM)

The mass of one mole of a substance expressed in grams, calculated by summing the relative atomic masses of all constituent atoms in the chemical formula.

Mole

The formula mass of a substance expressed in grams.

Concentration

A measure of the quantity of solute dissolved in a given volume of solution, typically measured in moles per litre ($\text{mol}\,l^{-1}$ or $\text{mol/l}$) using the relationship $\text{Moles} = \text{Volume (in litres)} \times \text{Concentration}$.

Standard Solution

A solution of accurately known concentration prepared by dissolving an accurately weighed mass of solute, transferring it and beaker rinsings into a standard flask, and adding deionised water to the calibration mark.