Chemistry IGCSE Y10

• Atomic mass is the average mass of an atom's nucleus.
• Isotopes are atoms with different numbers of neutrons but the same number of protons.
• The atomic number (Z) represents the number of protons in an atom.
• The periodic table is organized by atomic number.
• An element can have multiple isotopes, which differ only by their number of neutrons.
• Elements are classified based on their properties and behavior.
• Metallic bonding occurs when metal atoms lose electrons to form positive ions that attract delocalized electrons.
• Nonmetal elements have low melting points and boiling points compared to metallic elements.
• Metallic elements are shiny, malleable, ductile, good conductors of heat and electricity, have high melting points, and form positive ions when they react with other substances.
• Atomic Mass Units (amu): A unit used to measure the relative masses of atoms.
• Atomic Mass Units (amu): A unit used to measure atomic masses that are approximately equal to one-twelfth the mass of carbon-12.
• Isotopes are different forms of the same element with the same number of protons but different numbers of neutrons.
• Atomic radius decreases across a period due to increasing nuclear charge.
• Non-metal elements have low melting points due to weak intermolecular forces between molecules.
• Atomic structure refers to the arrangement of subatomic particles within an atom.
• When metals are in an electrical circuit, the electrons can move to the positive terminal while the negative terminal can supply electrons to the metal.
• Metals are also good conductors of heat as the delocalised electrons can move through the metal carrying the heat energy.
• Metals are malleable and ductile due to their metallic bonding as well.
• Layers of ions are able to slide over each other in metals due to their metallic bonding.
• The metallic bonds between the positive cations and negative electrons are not as strong as diamond (although still very strong).
• An element is a substance containing only one type of atom.
• A compound is a substance containing two or more types of atoms chemically joined together.
• A mixture can contain elements and compounds but the substances are not chemically joined.
• The structure of the atom is discussed in Topic 2.2, where it is stated that atoms consist of three sub-atomic particles called protons, neutrons and electrons.
• Protons are found within the very small core at the centre of the atom, known as the nucleus, and have a positive charge (+1) and a relative mass of 1 atomic mass unit (amu).
• There is one more positive charge (3 protons) than there are negative charges (2 electrons).
• Lithium becomes Li+ with a new electron arrangement of 2.
• A sulfur atom has 16 electrons and 16 protons, giving it an electron arrangement of 2,8,6.
• In order for sulfur to gain a full outer electron shell, it needs to gain 2 electrons.
• Sulfur gains two electrons and by doing so gains a full outer electron shell, giving it a stable electron arrangement.
• Sulfur now has eighteen electrons but still only has sixteen protons, meaning there are 2 more electrons than there are protons.
• There are two more negative charges (18 electrons) than there are positive charges (16 protons).
• An atom which has lost electrons becomes an ion with a positive charge.
• Metal atoms will lose electrons to become ions.
• An atom which has gained electrons becomes an ion with a negative charge.
• Non-metal atoms will gain electrons to become stable.
• Positive ions are known as cations.
• Negative ions are known as anions.
• Ionic bonding involves the formation of ions between a metal and a non-metal element.
• An ionic bond will form between a metal and a non-metal element.