CHEMISTRY: SELECTED ELEMENTS

CHEMISTRY: SELECTED ELEMENTS

1. Periodic table of elements

   • Matter is made up of particles. Particles making up a substance contains only atoms of the same type/kind then the substance is called an element. Most elements are solid at room temperature, only Mercury and Bromine are liquids, and 11 others are gases

2. ATOMS

   • Atomic number: is the number of protons in the nucleus of the atom Mass number: is the number of protons and neutrons in the nucleus of an atom
     • Protons are positvely charged
     • Electrons are negatively charged
     • Neutrons are netural charged/no charge
   • ISOTOPES
     • Atoms of the same element but differ in the number of neutrons in the nucleus
       • Therefore the physical properties of mass, density, boiling point and melting point for isotopes of the same element will differ due to the different number of neutrons in the nucleus
   • IONS
     • Atoms undergo chemical reactions to attain a full outer energy level and become energetically stable like a Noble Gas. It is the valence electrons of an atom that are involved in chemical reactions. Chemical properties of elements in the same group will thus be similar as they have the same number of valence electrons.
       • ELECTRON ARRANGEMENT: Electrons are found in energy levels around the nucleus of an atom. It is the electron arrangement of each atom that determines its chemical behaviour.
         • Explain why the electron arrangements for the fluorine atom and the magnesium atom are different, but the electron arrangements for the fluoride ion and the magnesium ion are the same. Fluorine and magnesium are atoms. They belong to different groups in the periodic table and different period and as a result have different electron arrangements F 2,7 , Mg 2,8,2 Fluorine is in group 17 and is in period 2. It has 7 valence electrons in its 2nd energy level whereas Mgagnesium is in group 2 and is in period 3. It has 2 valence elctrons in its 3rd energy level. Both F and Mg atoms require a full outer energy level like that of a noble gas, to be stable. Mg can achieve this by 2 loosing 2 valence electrons and becoming a magnesium ion (Mg2+) Mg--> Mg2+ 2e Fluorine can gin one electron and become fluoride ion (F-) F- +e --> F Both ions now have the same electronic arrangement both have 8 valence electrons in their outer energy level. They're isoelectronic and stable. Mg 2,8 , F 2,8 
         • 1st energy level 2 electrons 2nd energy level 8 electrons 3rd energy level 8 electrons
         • Period: Horizontal row Group: Vertical row
           • Elements in the same group have the same number of electrons in their outer energy level. Group 1 elements (Alkali Metals all have one outer energy level (valence) electron). Group 17 Halogens all have 7 outer electrons (7 valence electrons).
             • Potassium (K) is the most reactive metal out of Li and Na because its 1 valence electron is furtherest away from the positive nucleus (less electrostatic between protons and negative electrons) and thus can be more easily removed.
             • F is a more reactive halogen out of Cl because the F atom is smaller with 7 valence electrons in it's 2nd energy level and Cl has it's 7 valence electrons in it's 3rd energy level and as a result, the incoming electron (enabling F to have a full outer energy level) is more strongly acttracted to the positive nucleus.
             • Group 18 elements (Noble Gases) all have full outer energy levels and are thus energetically stable. All members except Helium (2 valence electrons) have 8 valence electrons
       • Isoelectronic is when atoms and ions have the same electron arrangement. They are different species as they have different charged and different number of protons in the nucleus
       • Ionic Bonding and Ionic Coumpound: Is the strongest electrostatic attraction between two oppositely charged ions eg between a sodium and chloride ion. When a metal atom reacts with a nonmetal atom, the metal atom transfers its valence electrons(s) to the nonmetal atom, which accepts the electrons and an ionic compound is formed. The resulting ions are more stable than the atoms they come from. There is a strong electrostatic attraction between these oppositely charged.
     • Atoms in Group 1 and Group 2 readily lose their valence electrons and become positively charged ions (cations). Atoms in Group 16 and 17 readily gain their valence electrons and become negatively charged ions (anions)

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