Presentation on theme: "Bonding. Formulas Chemical formulas Chemical formulas Tell us what elements a compound contains and the exact number of the atoms of each element."— Presentation transcript:
Formulas Chemical formulas Chemical formulas Tell us what elements a compound contains and the exact number of the atoms of each element in a unit of that compound Examples: SiO 2 1 atom of Silicon 2 atoms of Oxygen CH 3 COOH 2 atoms of Carbon 4 atoms of Oxygen 2 atoms of Oxygen
How do you know how many dots to make? Group 1 – 1 outer electron Group 2 – 2 outer electrons Group 3 – 12 – varies Group 13 – 3 outer electrons Group 14 – 4 outer electrons Group 15 – 5 outer electrons Group 16 – 6 outer electrons Group 17 – 7 outer electrons Group 18 – 8 outer electrons
Chemical Stability An atom is chemically stable when its outer energy level is complete. Atoms need 8 electrons to become stable. Exception – Hydrogen and Helium need only 2 electrons. Noble gases Stable since they have a complete outer energy level
Chemical Bonding Atoms with partially stable outer energy levels can gain, lose, or share electrons to obtain a stable outer energy level. They combine with other partially stable outer energy levels to get 8 electrons They become stable. An attraction forms between the atoms, pulling them together to form compounds Chemical bonds – the force that holds atoms together in a compound
Ions Atoms lose or gain electrons which are called ions. Ion Charged particle since it has more or fewer electrons than protons Loss of electrons – more protons Called cations Gain of electrons – less protons Called anions
Ions GroupValence Electrons Electrons Lost or GainedNumber of Electrons Lost or Gained Oxidation Number Group 11Lose1+1 Group 22Lose2+2 Group 133Lose3+3 Group 144Lose – Tin, Lead Gain/Share – Carbon, Silicon, 4+4 -4 Group 155Gain/Share3-3 Group 166Gain/Share2-2 Group 177Gain/Share1 Group 188Stable00
Ionic Bonding – The Givers and Takers Transfer of electrons between a metal and a nonmetal Metals – lose electrons and become a positive ion Nonmetals – gain electrons and become a negative ion The positive charge of the metal and the negative charge of the atom must be balanced. The compound is neutral.
Covalent Bonding – The Happy Couple The sharing of electrons between two nonmetals This sharing of electrons is called covalent bonding. Types of bonds Single bond – 2 shared electrons or 1 pair of electrons between atoms Double bond – 4 shared electrons or 2 pairs of electrons between atoms Triple bond – 6 shared electrons or 3 pairs of electrons between atoms
Metallic Bonding – “Sea of Electrons” The positively charged metallic ions are surrounded by a cloud of electrons Metallic ions are positively charged since metals tend to lose electrons. Electrons move freely among the positively charged ions
Unequal Sharing Electrons are not always shared equally between atoms in a covalent bond. Strength of the attraction is related to the size of the atom the charge of the nucleus the total number of electrons the atom has Electrons that are unequally shared are held more closely to the atoms with the larger nucleus.