yr 9

• The atomic structure and the periodic table are topics in chemistry.
• The simple model of the atom includes elements, compounds, equations, mixtures, the structure of the atom, size & mass of atoms, relative atomic mass, and electronic structure.
• Pure substances contain only one element or compound and are not mixed with anything else, for example, water that contains H2O molecules only is pure whereas if salt is added it then becomes impure.
• Arranging the elements in the periodic table is a topic in chemistry.
• The atomic number and mass number are also shown on the periodic table at CARBON.
• The symbol key for Carbon in the periodic table is C and the atomic number is 6.
• The elements Ha, No, Oo, Fo, Cl, Bro and lo must be written as molecules as they exist in nature as two atoms joined together.
• All substances are made of tiny particles of matter called atoms which are the building blocks of all matter.
• The electronic configuration for chlorine is: 2,8,7,4,2,3.
• Chlorine is in group 7, indicating that it has 7 outer electrons and requires 7 electrons to complete its outer shell.
• The position of chlorine on the Periodic Table is shown on page 32.
• The electronic configuration of the first 20 elements can be represented using either electron shell diagrams or written electronic configuration.
• The number of notations for a chlorine atom is 3, indicating that it has 3 shells of electrons.
• Each atom is made of subatomic particles called protons, neutrons, and electrons.
• The protons and neutrons are located at the centre of the atom, which is called the nucleus.
• The electrons move very fast around the nucleus in orbital paths called shells.
• The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located.
• The atom is the smallest part of an element that still retains the properties of the element.
• Groups are the vertical columns that show how many outer electrons each atom has and are numbered from 1 - 7, with a final group called group O (instead of group 8).
• The table is arranged in vertical columns called groups and in rows called periods.
• There are over 100 chemical elements which have been isolated and identified.
• Each element has one proton more than the element preceding it, so that elements end up in columns with other elements which have similar properties.
• Elements are arranged on the periodic table in order of increasing atomic number.
• Elements in period 2 have two electron shells, elements in period 3 have three electron shells.
• Group 4 elements have atoms with 4 electrons in the outermost shell, group 6 elements have atoms with 6 electrons in the outermost shell.
• Periods are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7.
• An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
• There is a limited number of elements, and all elements are found on the Periodic Table such as hydrogen, carbon, nitrogen.
• Each element is represented by its own unique symbol as seen on the Periodic Table, for example, N stands for nitrogen and for nitrogen only.
• Where a symbol contains two letters, the first one is always written in uppercase letters and the other in lowercase, for example, sodium is Na, not NA.
• The atomic number is unique to each element, so no two elements have the same number of protons.
• The PEN numbers for beryllium are thus: p=4, e=4, n=(9-4=)5.
• Both the atomic number and the mass number are given on the periodic table, but it can be easy to confuse them.
• The number of neutrons (n) can thus be calculated by subtracting the atomic number from the mass number.
• Electrons can be lost, gained, or shared during chemical processes but the proton number of an atom does not change in a chemical reaction.
• The atomic number and mass number for every element is on the periodic table.
• The mass number is the number of protons plus neutrons.
• Beryllium has an atomic number of 4, therefore it has 4 protons and 4 electrons.
• The mass number of beryllium is 9, it has 9 - 4=5 neutrons.
• The symbol for the mass number is A.