Grade 9 Chemistry

Atoms, Elements, and Compounds  

  1. Properties of Matter 

  • Matter is anything that has mass and takes up space.  

  • Chemistry is the study of matter and the changes, it undergoes 

  • Particle theory of matter: a theory that describes the composition and behaviour 

of matter 

1. All matter is made up of tiny particles that have empty spaces 

between them. 

2. Different substances are made up of different kinds of particles. 

3. Particles are in constant random motion. 

4. Th e particles of a substance move faster as its temperature increases. 

5. Particles attract each other. 

Pure substance: a substance that is made up of only one type of particle  

Ex: distilled water is only H2O  

Mixture: a substance that is made up of at least two different types of particles 

Ex: When you add a pinch of salt to a glass of distilled water, the salt dissolves 

and the water tastes salty. The water in the glass is no longer a pure 

substance but a mixture because it contains salt particles and water particles.  

A mechanical mixture is a mixture in which the substances in it 

are distinguishable from each other 

Ex: Breakfast cereal  

A solution looks like a pure substance but it contains more than one type 

of particle 

Ex: Apple juice  

Alloy: a solid solution of two or more metals 

  • Physical properties a characteristic of a substance that can be determined without changing the composition of that substance  

  • Physical properties give us information about what the substance is like. 

  • You can determine a physical property by simply observing the substance using your five senses and measuring instruments. 

  • Qualitative property a property of a substance that is not measured and does not have a numerical value, such as colour, odour, and texture 

  • quantitative property a property of a substance that is measured and has a numerical value, such as temperature, height, and mass 

  • Chemical Properties  

    A chemical property is a property of a substance that describes its ability to undergo changes to its composition to produce one or more new substances.  

    For example, bacterial cultures turn milk into cheese  

    Chemical Change  

    1. A change of colour  

    1. A change of odour  

    1. Bubbles are visible- a new substance is produced in the form of a gas 

    1. A new solid is seen- called a precipitate  

    1. A change in temperature  

Element- a pure substance that cannot be broken down into a simpler chemical substance by any physical or chemical means 

element symbol an abbreviation for a chemical element  

compound a pure substance composed of two or more different elements that are chemically joined 

metal an element that is lustrous, malleable, and ductile, and conducts heat and electricity 

non-metal an element, usually a gas or a dull powdery solid, that does not conduct heat or electricity 

metalloid an element that has properties of both metals and non-metals 

Chemical Families  

  • Elements in the same column of the periodic table belong to the same group, or chemical family.  

  • Families with distinctive properties have been given identifying names 

  1. Alkaline metals: have relatively low densities, very reactive, and soft  

  2. Alkaline Earth metals: less reactive than alkali metals but still reactive. They are harder than alkali metals 

  1. Transition metals: These metals are typically hard, dense, and shiny. They are good conductors 

  1. Halogens: Very reactive nonmetals  

  1. Noble gases: Very unreactive gases and very stable  

  1. Metalloids: have properties of both metals and nonmetals. Theories of the Atom  

    • Democritus 

    Greek philosopher Democritus proposed that all matter can be divided into smaller and smaller pieces until a single indivisible particle is reached. He named this particle the atom, which means “cannot be cut” 

    • Aristotle  

    He supported an earlier theory that all matter is made up of four basic substances: earth, water, air, and fire 

    The Billiard Ball Model- John Dalton  

    • Proposed the particle theory of matter  

    • This model was useful because it could explain many properties of matter. 

    Plum pudding model- J.J. Thomson  

    - Discovered the electron  

    - Thompson’s model was called the “plum pudding” model because the electrons embedded in an atom resembled the raisins in a plum pudding 

    The Gold Foil Experiment- Ernest Rutherford  

    • Discovered the proton  

    • In 1909, Ernest Rutherford's experiment showed that most particles passed through a thin gold foil, but some bounced back at large angles, suggesting a dense, positively charged center in the atom called the nucleus. This led Rutherford to conclude that atoms have a small, massive nucleus surrounded by a cloud of electrons, with most of the atom being empty space 

James Chadwick 

  • Discovered the neutron  

Neils Bohr 

  • Proposed that electrons orbit the nucleus in fixed paths with specific energy levels, similar to planets orbiting the Sun. 

  • The Bohr–Rutherford model of the atom consists of positively charged protons and neutral neutrons in the nucleus of an atom. Negatively charged electrons orbit the nucleus. 

  • Atomic number the number of protons in an atom’s nucleus 

  • mass number the number of protons and neutrons in an atom’s nucleus 

  • isotope an atom with the same number of protons but a different number of neutrons 

  • atomic mass the mass of an atom in atomic mass units (u)