Atomic Structure (u1)

• Alkali metals: These are all very reactive metal elements, found in group 1.
• Noble gases: The group 8 elements are known as the noble gases. They are a family of very unreactive elements.
• Halogens: Group 7 elements are known as the halogens. Like the alkali metals, these elements are also very reactive.
• Transition metals: The transition metals are found between groups 2 and 3 in the periodic table. These form the big rectangular block in the centre of the periodic table
• All substances are made up of tiny particles called atoms. An element contains only one type of atom.
• An atom contains a small positive nucleus surrounded by orbits of negative electrons.
• The nucleus contains two particles positive protons and neutral neutrons.
• Each element has its own unique number - atomic number. This identifies the element
• The atomic number of an element is the number of protons in its nucleus. As atoms are neutral because the number of protons (positive charge) equals the number of electrons (negative charge) this means the atomic number also gives the number of electrons in an atom.
• ATOMIC NUMBER = no. of protons = no. of electrons
• MASS NUMBER = no. of protons + no. of neutrons
• The first energy level of an atom can hold up to 2 electrons.
• The second and third levels of an atom can hold up to 8 electrons.
• Group 1 the ALKALI metals- All the alkali metals have 1 electron in their outer energy level. All are in Group 1 and have similar chemical properties.
• Group 7 the HALOGENS- All the halogens have 7 electrons in their outer energy level. All are in group 7 and have similar chemical properties.
• Group 8 the NOBLE GASES- All the noble gases have full outer energy level. They are very stable. Other elements react to achieve this electron arrangement.
• Isotopes are atoms with the same atomic number but different mass number.
• Many atoms react to form the electron arrangement of the nearest noble gas in the periodic table. Atoms react by either losing or gaining electrons (e-) to obtain the noble gas electron arrangement.
• Metal atoms tend to lose electrons forming positive ions.
• Non-metal atoms tend to gain electrons forming negative ions.
• An ion is an atom or a group of atoms that has an electric charge