CHEM1202 1.3- Density and Chemical Formulae

CHEM1201 General Chemistry

• Instructor: Dr. Sue Pyke

• Location: Room 3306, Physical Sciences building

• Contact: susan.pyke@flinders.edu.au

• Lecture: 3, Week 1

Density

• Definition of Density:

  • If one substance is more dense than another, it means one occupies the same space but is heavier.

• Density Formula:

  • Density = Mass/Volume

  • Units: g/cm³ = g/mL

  • Examples:

    • Water: 1.00 g/cm³

    • Silver: 10.49 g/cm³

    • Nitrogen: 0.00125 g/cm³

Density Calculations

• Calculating Density:

  • If mass and volume are known, density can be calculated.

  • Example Problem 1:

    • 10.0 g of sulfur fills a 5.0 mL vial.

    • Calculate density: Density = 10.0 g / 5.0 mL = 2.00 g/cm³.

  • Example Problem 2:

    • Ethylene Glycol (C2H6O2) density = 1.1 g/cm³, calculate mass for 56 L.

• Practice:

  • Week 1 tutorial questions and specified problems in Chapter 2.

Elements - Brief Introduction

• Definition of Elements:

  • Unique substances on the periodic table defined by different amounts of atomic components.

Atomic Structure

• Components of Atoms:

  • Protons: Positively charged in the nucleus.

  • Neutrons: Neutral, located in the nucleus.

  • Electrons: Negatively charged, orbiting the nucleus.

Atomic Properties

• Atomic Number (Z):

  • Defines the element by the number of protons.

• Importance of Chemical Symbols:

  • Helps identify elements (e.g., Al = Aluminium, Cu = Copper).

Periodic Table Overview

• Key Features:

  • Chemical Symbol:

    • Uppercase first letter, lower case second (if present).

  • Atomic Mass: Average mass per mole.

  • Ions: Atoms with unequal protons and electrons, not electrically neutral.

Chemical Formulae

• Definition of Chemical Formulae:

  • Indicate types and numbers of atoms in a compound.

• Examples:

  • Water: H2O

  • Calcium Chloride: CaCl2

  • Aluminium Chloride: AlCl3

Determining Ratios

• Predicting Combinations:

  • Use valency table to determine how atoms combine for neutrality.

  • Example: Al contributes 3+, needs three Cl (1- each) for AlCl3.

Polyatomic Ions

• Definition: Groups of atoms acting as a unit.

• Examples:

  • Calcium Carbonate: CaCO3

  • Calcium Hydroxide: Ca(OH)2 (contains brackets for multiple polyatomics).

Importance of Chemical Formulae

• Uses:

  • Essential for describing compound proportions.

  • Writing chemical equations.

  • Calculating molar masses.

• Main Features of Compounds:

  • Elements in fixed proportions; neutral compounds with equal positive and negative parts.

• Names of Compounds:

  • Typically end in -ide for a single type of atom.

Writing Chemical Formulae

• Order of Atoms:

  • Positive atoms/groups come first, followed by negative ones.

• Example of Neutral Compound:

  • Nitrogen and hydrogen (N3- and H+) combine to form NH3 (ammonia).

Non-neutral Compounds

• Examples of Non-neutral Formulas:

  • NH3 (ammonia) is neutral.

  • NH4+ (ammonium ion) is not neutral.

• Combining for Neutral Compounds:

  • Examples include Ammonium Chloride, Ammonium Carbonate.

Periodic Table and Valencies

• Valency Prediction:

  • Easier to determine from the periodic table.

• Transition Elements:

  • Can exhibit multiple valencies (e.g., Fe2+ and Fe3+).

• Polyatomic Ions:

  • Often require memorization (e.g., NO3-).

Understanding Chemistry

• Chemistry is about connecting many pieces of information to create a comprehensive understanding.