Stability in Bonding

A chemical formula tells us what elements are contained in a compound, and the exact number of atoms there are in a unit of that compound. Ex – H 2 0 = 2 atoms of Hydrogen and 1 atom of Oxygen Hydrogen Oxygen

The small number after an element ’ s symbol is called a subscript. The subscript identifies the number of atoms of the element that comes BEFORE it. H20H20 Subscript

SiO 2 is made of 1 atom of silicon and 2 atoms of oxygen HC 2 H 3 O 2 (vinegar) is made of __ atoms of Hydrogen, ___ atoms of Carbon, and ___ atoms of oxygen.

SiO 2 is made of 1 atom of silicon and 2 atoms of oxygen HC 2 H 3 O 2 (vinegar) is made of 4 atoms of Hydrogen, 2 atoms of Carbon, and 2 atoms of oxygen.

Atoms form compounds because they want to become more stable.

A chemical bond is the force that holds atoms together in a compound.

All atoms want 8 valance electrons, and they will share electrons with other elements in order to reach the goal of 8. Group 1 will bond with Group 17 Group 2 will bond with Group 16

The Nobel gases (group 18) are the only elements who naturally have 8 valence electrons. They will never form compounds and are considered INERT (non reactive).

Types of Bonds (page 580)  Atoms gain or lose electrons in order to become more stable (to reach 8 valence electrons).  An Ion is an atom that has gained or lost an electron.  Ions are charged (+ or -) particles because their number of electrons no longer equals their number of protons.

Ions Potassium Ion (K + ) – has more PROTONS than ELECTRONS. Potassium (K) (as appears on Periodic Table)

When it gives away an electron during bonding, potassium becomes positively charged because there are 19 protons but only 18 electrons. We write the potassium ion like this: K+ The + sign indicates a positive charge.

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Ionic bond – a bond between elements of opposite charges. Na has 1 valence electron Chlorine has 7 valence electrons The 2 elements are attracted to each other Na gives its valence electron to Cl. Now both join to form the compound NaCl. They are held together by an ionic bond. Since the charges balance one another, the overall compound is neutral.

Covalent Bonds Another way atoms can reach the magic number of 8 valence electrons is by sharing electrons. Hydrogen has 1 valence electron Oxygen has 6 valence electrons. They are attracted to one another and share electrons so that each has 8 total. Covalent bonds are made when atoms share electrons. The result of a covalent bond is a molecule.

Sometimes molecules have atoms that don ’ t share their electrons equally. A molecule that has a slight positive charge at one end and a slightly negative charge at the other is called a polar molecule. Water is polar. A non-polar molecule does not have a charge because they form COVALENT BONDS.

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Last one… I promise!