All substances are made of atoms and a substance made up of one type of atom is called an element. There are about 100 different elements and these elements are shown in the periodic table. Metals are found on the left side of the periodic table and non metals are found on the right side. The groups contain elelments elelment with similar properties.
Atoms of each element are represent by a chemical symbol. E.g. O represents oxygen. You don't need to know the chemical symbols for elements if they are not named in the specification syllabus.
The Nucleus of the atom contains protons and neutrons. It is positively charged, very dense, very small, nearly all of the mass of the atom is concentrated in the nucleus.
The Electron Cloud virtually has no mass. It is deformable and it is negatively charged and contains electrons.
The relative electrical charge for a proton is +1, neutron is 0 and electron is -1. In a neutral atom, the number of electrons is equal to the number of protons in the nucleus. Therefore atoms have no overall electrical charge ie overall neutral.
All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons. Elements consist of one type of atom only.
The number of protons in an atom of an element is its atomic number.
The sum of the protons and neutrons in an atom is its mass number.
Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells). You can use the term energy level or shell for where an electron is.
You should be able to represent the electronic structure of the first 20 elements of the periodic table in the following forms e.g sodium 2,8,1
The Periodic Table
Elements in the same group in the periodic table have the same number of electrons in their highest energy level (outer electrons) and this gives them similar chemical properties.
Vertical columns of similar elements are called groups. They are similar because they have the same outer electron structure - same number of outer electrons.
The elements in Group 0 of the periodic table are called the noble gases. The noble gases have eight electrons in their outer energy level, except for helium, which has only two electrons. The noble gases are unreactive because their atoms have a very stable electron arrangements.
When elements react, their atoms join with other atoms to form compounds. This involves giving, taking or sharing electrons to form ions or molecules. Compounds formed from metals and non-metals consist of ions (electrically charged particles) - hence called ionic compounds.
Metals lose electrons to form positive ions, whereas non-metals gain electrons to form negative ions - but only in terms of single electron transfers. E.g. metallic sodium forms a sodium ion by electron loss: Na ==> Na+ + e- , and non-metal chlorine atoms form a chloride ion by electron gain: Cl + e- ==> Cl-. Compounds formed from non-metals consist of molecules. In molecules the atoms are held together by covalent bonds, hence know as covalent compounds.
Chemical reactions can be represented by word equations or by symbol equations.
No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants. This is known as the law of conservation of mass. In terms of masses involved of chemical reactions, you only need to appreciate law of conservation of mass.