8.3 Chemistry Notes

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Atomic Structure

neutrons

neutrons are neutrally charged

they make up the nucleus (with protons)

protons

protons are positively charged

they make up the nucleus (with neutrons)

electrons

electrons are negatively charged

they orbit the nucleus in specific energy levels

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Electron Configuration

electrons exist within the "electron cloud" around the nucleus

they are restricted to particular areas within the electron cloud known as "energy levels"

each energy level has a maximum number of electrons that can fit

Configuration

1st energy level = 2 electrons

2nd energy level = 8 electrons

3rd energy level = 8 electrons

4th energy level = 18 electrons

Notes on configuration

electron configuration is written as numbers separated by commas

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Periodic Table of Elements

*an element is a substance at consists of only one type atom

-----> it cannot be broken down into a simpler substance rough chemical reaction (but it can through nuclear reactions)

118 elements (118 different types of atoms that we know of so far...)

------> 92 are natural

-------> more synthetic elements are being made in labs every year

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Interpreting Chemical Formulas

Why do atoms form bonds?

*noble gases (Group 18) don't form bonds because they have a full outer (valence) energy level

Metals

bond with other atoms by giving them their valence electrons

Non - Metals

bond with other atoms by taking or sharing their valence electrons

Other

Atoms bond to attain a more stable electron configuration (i.e. full valence energy level)

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Compounds and Molecules

atom: smallest particle of an element that retains its chemical identity (the number of protons determines which element it is)

element: a substance which consists of one type of atom

------------> an atom of an element

------------> a molecule of an element

molecule: a group of non - metal atoms bonded together in a fixed ratio

compound: a substance made of atoms of different elements bonded in a fixed ratio

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Chemical Formulas

chemical formulas are a shorthand way to represent a molecule or compound using:

-----------> symbols: type of atoms present, (first letter always a capital and second letter lower case)

----------> subscript numbers: ratio of each type of atom in the molecule / compound (they only apply to the atom beforehand)

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Pure substances vs. Mixtures

Pure substances contain only one type of particle therefore has a consistent chemical composition

Mixtures contain two or more different particles, (elements or compounds) which are NOT chemically bonded and therefore do not have a consistent composition ( a definite ratio)

mixtures can be separated physically

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Physical and Chemical change

a physical change is when some of the properties of a substance changes but the chemical composition doesn't change

Changes may include:

shape

size

state (solid, liquid, gas)

How does a substance change state?

When a substance is heated, the particles gain energy and begin to move faster. The particles will spread out and take up more space. With additional heat energy, the particles will start to move so quickly that the attractive forces between the particles weaken. Eventually, the attractive forces are weakened enough for the substance to change state