Science Grade 9 Exam Notes

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Chemistry

Types pf Compounds

* Homogeneous mixtures are composed of one or more parts that look as one. * Heterogeneous mixtures consist of two or more substances and do not look as one. * Compounds are two or more elements that are chemically combined. * Matter that contains more than one kind of particle.

* Elements are pure substances that cannot be broken down into smaller parts. * Solutions are a mixture of one or more substances and is homogeneous. * Pure substances contains one kind of particle.

* Mechanical Mixtures area mix of substances that is heterogeneous. Phsical and Chemical Properties
Physical Properties

* Physical Property- a characteristic of a substance that can be observed and measures without changing the identity of the substance. * Qualitative Physical Properties: Colour, Smell, State (solid, liquid, gas), texture, lustre (shiny, dull), malleability (soft, pliable, hard). * Quantitative Physical Properties: Viscosity, Melting Point, Boiling Point, Solubility, Hardness, Conductivity, Density. Chemical Properties

* Chemical Property- the ability of a substance to change and form new substances. * Chemical Reactivity- With water, oxygen, acids, or another pure substance. * Combustibility- the ability of a substance to burn in air * Stability- the ability of a substance to remain unchanged. * Toxicity- the ability of a substance to cause harmful effects in plants and animals. Signs

1. Heat is produced.
2. Colour changes.
3. Bubbles form.
4. Precipitate forms(white specs at the bottom of the container). In Contrast
Physical PropertiesChemical Properties
* size, shape, color, temperature, texture, and weight.
* Never changes forms.
* Can be observed without changing identity.

* Two substances reacting on act other.
* Things that we cannot sense with our seances.
* Changes and forms new substances.

Density Formula

Mass
Density = Volume
Evolution of the Atomic Model

Democritus - the Greek philosopher that proposed the atom.
Dalton - proposed a theory that atoms cannot be broken/broken down, they can form compounds, and atoms are different for every single element. Thompson - discovered the electron and that all atoms had negatively charged particles. Proposed that the atom was a lump of positively charged material, with electrons inserted throughout. (Raisin Bread Model). Rutherford - proposed that all atoms had a nucleus. Shot alpha particles at gold foil, and some bounced back, therefore, he inferred that there must be a small region of positive particles; the nucleus. Bohr - discovered the energy levels in the atom, stating that only a certain amount of electrons can be on these levels at once, and that they can move from level to level, the electron has to absorb a certain energy level.Chadwick- British physicist that once work with Rutherford, was the first person to experimentally show that neutral particles (neutrons) help make the nuclei of most atoms. He was awarded the Nobel Prize in 1935. Atomic Structure

Mass Number- The sum of the number of protons and neutrons in the nucleus of an atom. Atomic Mass Number- The number of Protons in the nucleus of an atom. Valence Electrons- An electron in the outmost occupied energy level of an atom.

Periodic Table

Developed

In the 1860's a Russian chemist named Dimitri Mendeleev organized known elements looking for patterns in their properties. He put them in order of atomic mass. Mendeleev left gaps in his table wherever there seemed to be a break in the pattern of the properties.

Classes

Metals are located to the left of the zig zag line. Good conductors of electricity and heat. they are malleable and ductile. About 80 elements are metals. Non Metals- located to the right of the zig zag line. Brittle, dull; not ductile or malleable. Poor conductors of heat and electricity. Only 18 elements are nonmetals...
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