Science test

Summary Sheet For Science Test

Periodic Table Trends – Test Notes

🔹 Periodic Table Basics:

• Organized by atomic number (protons).

• 18 groups (columns ↓), 7 periods (rows →).

• Group (↓) = column (same valence electrons).

• Period (→) = row (same number of electron shells).

🔹 Group Trends (↓):
✅ Atomic mass increases down a group.
✅ Number of electron shells increases down a group.
✅ Same number of valence electrons in a group.

🔹 Period Trends (→):
✅ Atomic mass generally increases left to right.
✅ Valence electrons increase left to right.
✅ Same number of electron shells (equal to period number).

📌 Remember: Period number = Number of electron shells!

Classification of Matter – Test Notes

🔹 Matter → Anything that takes up space and has mass.

1. Pure Substances

✅ Contain only one kind of particle (atom or molecule).
✅ Cannot be separated by physical means.
✅ Examples: Gold, sugar, pure water.

🔸 Elements

• Cannot be broken down into simpler substances.

• Made of a single type of atom (found on the periodic table).

• Examples: Gold (Au), Zinc (Zn), Copper (Cu), Iron (Fe).

🔹 Metals (Left & Center of Periodic Table)

• Examples: Gold, Zinc, Copper, Iron.

🔹 Non-Metals (Right Side of Periodic Table)

• Examples: Oxygen (O), Nitrogen (N), Helium (He).

🔸 Compounds

• Contain two or more different elements in a fixed proportion.

• Examples: Sugar, Water (H₂O), Salt, Baking Soda, CO₂.

2. Mixtures

✅ Contain two or more pure substances.
✅ Can be separated by physical means.
✅ Examples: Alloy, sea water, tea, tap water, granola bar.

🔸 Homogeneous Solutions

• Uniform mixture (cannot see different parts).

• Examples: Sea water, alloys, tap water, tea.

🔸 Heterogeneous Mixtures (Mechanical Mixtures)

• Different parts can be clearly seen.

• Examples: Granola bar, lemonade (with pulp), salad.

📝 Key Differences:

• Pure Substances = One kind of particle.

• Elements = One type of atom.

• Compounds = Two or more different elements.

• Mixtures = Two or more pure substances.

  • Homogeneous = Looks the same throughout.

  • Heterogeneous = Different parts visible.

How to Count Atoms – Test Notes

🔹 Chemical Symbol → Represents one atom of an element.

• Example: Na = 1 sodium atom.

🔹 Subscript → Small number at the lower right of an element symbol.

• Indicates the number of atoms of that element.

• Example: H₂ = 2 hydrogen atoms.

🔹 Coefficient → Large number in front of a chemical formula.

• Multiplies the number of atoms of each element in the formula.

• Example:

  • 2H₂O → 4 hydrogen atoms, 2 oxygen atoms.

  • 3CuSO₄ → 3 copper (Cu), 3 sulfur (S), 12 oxygen (O).

  • 4Pb(NO₃)₂ →

    • 4 lead (Pb),

    • (NO₃)₂ means 2 nitrogen (N) & 6 oxygen (O) per molecule

    • Multiply by 4: 8 nitrogen (N), 24 oxygen (O).

✅ REMEMBER:

• Subscript applies only to the element before it.

• Parentheses ( ) → Apply the subscript to everything inside.

• Coefficient multiplies everything in the formula.

Inside the Atom – Test Notes

Types of Subatomic Particles

Atoms are made of 3 subatomic particles:

1⃣ Proton (p⁺) → Positive charge (+1)

• Mass: 1 atomic mass unit (amu)

• Location: Inside nucleus

2⃣ Neutron (n⁰) → Neutral (no charge)

• Mass: 1 atomic mass unit (amu)

• Location: Inside nucleus

3⃣ Electron (e⁻) → Negative charge (-1)

• Mass: ~1/1836 of a proton (very small)

• Location: Electron shells orbiting the nucleus

✅ Atoms are electrically neutral, meaning:

# of Protons = # of Electrons

Atomic Number

🔹 The atomic number = number of protons in an atom.
🔹 Determines the element's identity on the periodic table.
🔹 In a neutral atom, the # of protons = # of electrons.

✅ REMEMBER:

• Atomic number = # of protons = # of electrons (if neutral)

• Mass number = Protons + Neutrons

• Neutrons = Mass number - Atomic number