Year 9 AQA GCSE Chemistry Atomic Structure PDF

# Year 9 AQA GCSE Science (CHEMISTRY) ## Topic 2: Atomic Structure ### 4.1.1 Atoms, elements and compounds #### 4.1.1.1 Atoms, elements and compounds - All substances are made of atoms. - An atom is the smallest part of an element that can exist. - Atoms of each element are represented by a chemical...

# Year 9 AQA GCSE Science (CHEMISTRY) ## Topic 2: Atomic Structure ### 4.1.1 Atoms, elements and compounds #### 4.1.1.1 Atoms, elements and compounds - All substances are made of atoms. - An atom is the smallest part of an element that can exist. - Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, Na represents an atom of sodium. - There are about 100 different elements. - Elements are shown in the periodic table. - Compounds are formed from elements by chemical reactions. - Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change. - Compounds contain 2 or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed. - Compounds can only be separated into elements by chemical reactions. - Chemical reactions can be represented by word equations or equations using symbols and formulae. **Students will be supplied with a periodic table for the exam and should be able to:** - Use the names and symbols of the first 20 elements in the periodic table, the elements in Groups 1 and 7, and other elements in this specification. - Name compounds of these elements from given formulae or symbol equations. - Write word equations for the reactions in this specification. - Write formulae and balanced chemical equations for the reactions in this specification. - (HT only) Write balanced half equations and ionic equations where appropriate. ### 4.1.1.2 Mixtures - A mixture consists of two or more elements or compounds not chemically combined together. - The chemical properties of each substance in the mixture are unchanged. - Mixtures can be separated by physical processes such as filtration, crystallization, simple distillation, fractional distillation and chromatography. - These physical processes do not involve chemical reactions. **Students should be able to:** - Describe, explain and give examples of the specified processes of separation. - Suggest suitable separation and purification techniques for mixtures when given appropriate information. ### 4.1.1.3 Scientific models of the atom (common content with physics) - New experimental evidence may lead to a scientific model being changed or replaced. ### 4.1.1.4 Relative electrical charges of subatomic particles - The relative electrical charges of the particles in atoms are: - Name of particle | Relative charge - Proton | +1 - Neutron | 0 - Electron | -1 - In an atom, the number of electrons is equal to the number of protons in the nucleus. - Atoms have no overall electrical charge (they are neutral). - The number of protons in an atom of an element is its atomic number. - All atoms of a particular element have the same number of protons. - Atoms of different elements have different numbers of protons. **Students should be able to:** - Use the atomic model to describe atoms. ### 4.1.1.5 Size and mass of atoms - Atoms are very small, having a radius of about 0.1 nm (1 x 10^-10 m). - The radius of a nucleus is less than 1/10 000 of that of the atom (about 1 x 10^-14 m). - Almost all the mass of an atom is the nucleus. ## Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided. - The discovery of the electron led to the plum pudding model of the atom. - The plum pudding model suggested that the atom was a ball of positive charge with negative electrons embedded in it. ## The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model. - Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. - The theoretical calculations of Bohr agreed with experimental observations. - Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. - The name proton was given to these particles. ## The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea. **Students should be able to:** - Describe the difference between the plum pudding model of the atom and the nuclear model of the atom. - Describe why the new evidence from the scattering experiment led to a change in the atomic model. *Details of experimental work supporting the Bohr model are not required. Details of these experiments are not required. Details of Chadwick's experimental work are not required.*