Notes on Atoms, Elements, and Compounds
AQA GCSE Chemistry Unit 1
C 1: Fundamental ideas:
C 1.1. Atoms, elements and compounds: * All substances are made up of atoms. * Elements contain only one atom. * Compounds contain more than one atom. * An atom has a tiny nucleus in its centre, surrounded by electrons.
C 1.2. Atomic structure: * Atoms are made up of protons, neutrons and electrons. * Protons and electrons have equal and opposite electrical charges. Protons are positively charged, and electrons are negatively charged. * Neutrons have no electrical charge. They are neutral. * Atomic number = number of protons (number of electrons.) * Mass number = number of protons and neutrons. * Atoms are arranged in the periodic table in order of their atomic number.
C 1.3. The arrangement of electrons in atoms: * The electrons in an atom are arranges in energy levels or shells. * Atoms with the same number of electrons in their outermost shell belong in the same group of the periodic table. * The arrangement of electrons in the outermost shell of an elements atom determines the way that element reacts. * The atoms of the unreactive noble gases (in group 0) all have very stable arrangements of electrons.
C 1.4. Forming bonds: * When atoms from different elements react together they make compounds. The formula of a compound shows the number and type of atoms that have bonded together to make that compound. * When metals react with non-metals, charged particles called ions are formed. * Metal atoms form positively charged atoms. Non-metals form negatively charged atoms. These oppositely charged ions attract each other in ionic bonding. * Atoms of non-metals bond to each other by sharing electrons. This is called covalent bonding.
C 1.5. Chemical equations: * As no new atoms are ever created or destroyed in a chemical reaction: total mass of reactants = total mass of products. * There is the same number of each type of atom in
C 1: Fundamental ideas:
C 1.1. Atoms, elements and compounds: * All substances are made up of atoms. * Elements contain only one atom. * Compounds contain more than one atom. * An atom has a tiny nucleus in its centre, surrounded by electrons.
C 1.2. Atomic structure: * Atoms are made up of protons, neutrons and electrons. * Protons and electrons have equal and opposite electrical charges. Protons are positively charged, and electrons are negatively charged. * Neutrons have no electrical charge. They are neutral. * Atomic number = number of protons (number of electrons.) * Mass number = number of protons and neutrons. * Atoms are arranged in the periodic table in order of their atomic number.
C 1.3. The arrangement of electrons in atoms: * The electrons in an atom are arranges in energy levels or shells. * Atoms with the same number of electrons in their outermost shell belong in the same group of the periodic table. * The arrangement of electrons in the outermost shell of an elements atom determines the way that element reacts. * The atoms of the unreactive noble gases (in group 0) all have very stable arrangements of electrons.
C 1.4. Forming bonds: * When atoms from different elements react together they make compounds. The formula of a compound shows the number and type of atoms that have bonded together to make that compound. * When metals react with non-metals, charged particles called ions are formed. * Metal atoms form positively charged atoms. Non-metals form negatively charged atoms. These oppositely charged ions attract each other in ionic bonding. * Atoms of non-metals bond to each other by sharing electrons. This is called covalent bonding.
C 1.5. Chemical equations: * As no new atoms are ever created or destroyed in a chemical reaction: total mass of reactants = total mass of products. * There is the same number of each type of atom in