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Bonding

Bonding. 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.

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Bonding

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  1. Bonding

  2. 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: • SiO2 • 1 atom of Silicon • 2 atoms of Oxygen • CH3COOH • 2 atoms of Carbon • 4 atoms of Oxygen • 2 atoms of Oxygen

  3. Electron Dot Structures • Show only the electrons in the outer energy level of an atom • Electrons also called valence electrons • Chemical symbol surrounded by dots representing its outer electrons

  4. 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

  5. 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

  6. 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

  7. Ions • Atoms lose or gain electrons which are called ions. • Ion • Charged particle since it has more of fewer electrons than protons • Loss of electrons – more protons • Called cations • Gain of electrons – less protons • Called anions

  8. Ions

  9. 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.

  10. 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

  11. 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

  12. 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.

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