# Atoms and moleculesPage 1

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## What is an atom mostly made of?

A) The nucleus

B) Electrons

C) Empty space (nothing)

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What is an atom mostly made of?

A) The nucleus

B) Electrons

C) Empty space (nothing)

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## The sizes of things in an atom

The nucleus of an atom is very small compared to the size of the atom

Electrons are also very small compared to protons and neutrons

If a proton were the size of a marble, an electron would be about the width of a human hair, and the electron would be about 4 kilometers away from the proton.

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## The Rutherford Model of the Atom

The “Rutherford Model” of the atom is a simple way of thinking of an atom

It is not correct in some ways

In the Rutherford Model, electrons move around (orbit) the nucleus like planets moving around the sun

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## Probability

Probability is the chance that something will happen

It is a number between 0 (definitely won’t happen) to 1 (definitely will happen)

If I roll a 6-sided die, the probability of rolling a 6 is 1/6 (0.167). It is the same probability for rolling any of the numbers on the die.

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## Electron Orbitals

Electrons have a certain probability of being in a certain place at any time.

This probability has a shape called an “orbital”

We don’t really know where electrons are at any time, but we know their orbitals (where they might be)

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## Ions

An ion is an atom or molecule in which the # of electrons is not equal to the # of protons

This gives the atom an overall positive or negative electrical charge

If it has a positive charge its called a cation.

If it has a negative charge its called an anion.

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A mole is the amount of any substance that has an Avogadro’s constant (6.022×1023) atoms or molecules

“Mole” is also the name of an animal that lives underground

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