CHEM-1

### Atomic Number & Mass Number

- Atomic number = number of protons

- Mass number = protons + neutrons

- Isotopes = atoms of the same element with different numbers of neutrons

### Organization

- Elements arranged by increasing atomic number

- Groups = columns (same number of outer electrons, similar reactivity)

- Periods = rows (same number of electron shells)

### Key Groups

- Group 1 (Alkali metals): very reactive, soft, low melting points

- Group 7 (Halogens): reactive non-metals, form salts

- Group 0 (Noble gases): unreactive, full outer shell

## Chemical Bonding

### Ionic Bonding

- Between metal and non-metal

- Electrons transferred

- Forms charged ions (positive metal, negative non-metal)

### Covalent Bonding

- Between two non-metals

- Electrons shared

- Molecules formed, not ions

### Metallic Bonding (basic)

- Metal atoms share delocalised electrons

- Strong bonds, high melting points, good conductors

### Types of Reactions

- Combustion: burning in oxygen

- Neutralisation: acid + base → salt + water

- Displacement: more reactive element replaces a less reactive one

- Decomposition: compound breaks into simpler substances

### Indicators

- Litmus: red in acid, blue in base

- Universal indicator: full color range (strong acid = red, strong base = purple)

### Reactions

- Acid + metal → salt + hydrogen

- Acid + base → salt + water

- Acid + carbonate → salt + water + CO₂

## The Mole (basic intro)

- One mole = 6.022 × 10²³ particles

- Molar mass = relative atomic/molecular mass in grams

### Ions

- Positive ion: loses electrons (more protons than electrons)

- Negative ion: gains electrons (more electrons than protons)