10 - Snc2d1 - General Sciences

Chemistry

Periodic table

Periods: horizontal
Families or groups: vertical

• Reactivity generally increases for cations as you move down the table e.g. K is more reactive than Na
  • Electrons further from the nucleus are more easily lost, leading to faster reactions
    • Like a magnet: further away, lesser attraction
• Reactivity for anions generally decreases as you move down
  • Anions gain electrons, so the closer the shell is to the orbital, the faster they gain electrons

Ions

Important

Ion - a charged entity formed when atoms gain or lose electrons (to become stable)

• Similar properties but different atomic masses

• An ion is an atom that has lost or gained electrons

• Elements with full valence shells are non-reactive (stable)

• Atoms can gain, lose, or share electrons to become stable

• Cations and Anions:

  • Metals are likely to lose electrons and form positive ions called cations
  • Non-metals are likely to gain electrons and form negative ions called anions
  • Cations:
    • Naming: metal name + “ion”
  • Anion:
    • Naming: non-metal name - ending + “ide”

Definitions

• Iso: the same
• Electronic: electron arrangement (e.g., identical Bohr diagrams minus the nucleus)
• Isoelectric: atoms/ions that have the same electron arrangement as another atom/ion

Diagrams

• Lewis: unpaired valence electrons can be shared

Formulas

In the formula Gold (I) Chloride, 1 represents the positive charge of gold (a cation).

Chemical reactions

• Physical changes occur during chemical reactions
• Physical changes affect state or form but do not change the original substance

5 signs of chemical reactions

1. Release of gas
2. Release of light
3. Change in heat
4. Formation of precipitate (a solid)
5. Unexpected color change

All chemical reactions convert reactants into products with different properties than the reactants.

• If there are chemical changes, the reaction is chemical. If not, it’s physical.

Types of Chemical Reactions

• Endothermic = reactants + heat

Chemical Equations

A chemical equation uses words, symbols, or formulas to describe changes during a chemical reaction.

• Balancing Chemical Equations
  The mass of products and reactants must be the same.

• NO atoms are destroyed or created during a chemical reaction; atoms are rearranged to form products. Chemical bonds between atoms are broken and new ones form.
  Atoms reconnect in new ways.

Rules for balancing:

• Use only whole numbers
• Ensure coefficients in the equation are the lowest common factor
• Never change a subscript in a formula to balance atoms

Hints for balancing:

• Balance atoms in complicated formulas first, and balance pure elements last
• Hydrogen and/or oxygen often appear in most reactants and products; balance other elements first, then hydrogen (second to last) and oxygen (last)

Example: If NO₃ appears in reactants and products, count NO₃ rather than N and O separately.

• Word equation: Hydrogen gas + Oxygen gas → Water
• Formula equation: H₂ + O₂ → H₂O

Every chemical equation must have:

1. Two or more reactants
2. One or more products
3. An arrow to show conversion
4. Plus signs to split multiple products or reactants

Possible states of matter in chemical equations:

• S - solid (all metals, except mercury)
• G - gas
• Aq - aqueous (dissolved in water; all ionic compounds unless they end in oxide, then it’s solid)
• l Liquid

Example: $H_2(g)+O_2(g)\to H_{2}O(l)$

Catalysts

A substance that speeds up a reaction without being consumed.
Often shown above the arrow in an equation.

Memorization:

• D
• H₂O - Water
• NH₃ - Ammonia
• CH₄ - Methane

H O F Br I N Cl

• Hydrogen - Gas
• Oxygen - Gas
• Fluorine - Gas
• Bromine - Liquid
• Iodine - Solid
• Nitrogen - Gas
• Chlorine - Gas