1. Substances and Atomic Structure
Understanding the fundamental building blocks of is crucial. Substances are made of atoms, which are the basic units of elements. Elements are represented in the periodic table by symbols (e.g., H for hydrogen, O for oxygen).
A compound consists of two or more different of atoms bonded chemically (e.g., H₂O for water, with 2 hydrogen and 1 oxygen atom). The number after a symbol indicates how many atoms are present; if no number, it’s assumed to be1.
Atoms are involved in chemical reactions where bonds are broken and formed, but atoms are neither created nor destroyed (law of conservation of mass). Reactions are represented by word equations and chemical equations, which must be balanced to ensure same number of each atom on both sides.
2. Balancing Chemical Equations
Start by balancing atoms that appear in only one compound. For example, carbon first, then hydrogen, then oxygen. Use coefficients (numbers in front of formulas) to multiply the number of atoms, not subscripts within formulas.
Example: Balancing combustion of methane (CH₄ + 2O₂ →₂ + 2H₂O)
3. Mixtures and Separation Techniques
Mixtures are combinations of elements and compounds not bonded chemically. Examples include air (a of gases) and salt water (a solution).
Separation methods include:
Filtration: separates insoluble solids (e.g., sand from water).
<>Crystallization: leaves behind dissolved solids after evaporation.
Distillation: heats the mixture; components with different boiling points condense separately (fractional distillation for multiple liquids).
4. States of Matter and
Water exists in three states:
Solid (ice): particles vibrate in fixed positions.
Liquid (water): particles touch but move freely.
Gas (water vapor): particles are far apart and move rapidly.
Physical changes involve state changesmelting, boiling, condensing) without forming new substances. Energy (heat) is supplied or removed during these processes.