Chapter 6

State Standards:3.a; 7.b

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The Atom

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There have been many changes that have contributed to what the atomic theory is today

Over centuries many scientist have discovered and clarified information about the atom

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The atom is the smallest particle within an element

An element is made-up of MANY atoms that are exactly the same

Atoms cannot be seen with the naked eye

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It would take 106 million billion Au atoms to cover the surface of a dollar bill70 million He atoms could fit on

your pencil eraser Contreras

Nucleus – small, dense, positively charged center Protons – positively charged particles

in the nucleus Neutrons – particles in the nucleus with

no charge

Electrons – negatively charged particles found in electron clouds outside the nucleus. Determines size of atom.

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Electron Cloud

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Protons 1 amu Positively charged (+)

Neutron 1 amu No charge

The nucleus is the biggest part of the atom

1 amu = 0.0000000000000000000000017 g

Atomic Mass Unit (amu)

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If there was a nucleus the size of a grape, it would have a mass of 9 million metric tons (18 million pounds)!Contreras

Electrons Negatively charged (-) Found only in electron clouds Smallest mass particle of the atom 1/1800 size of proton and neutron

Electron Cloud Region outside the nucleus where

electrons are contained

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Atoms and Elements

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1. Gravitational Force – holds all the parts of the atom together

2. Electromagnetic Force – attracts electrons (-) around nucleus (+)

3. Strong Force – holds protons in nucleus together

4. Weak Force – holds nucleus together in radioactive atoms

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Nucleus has a positive charge (because of protons)

Electrons have negative charge

For an atom to have no charge, positive and negative charges need to be balanced (# of protons and electrons is equal)

An ion is an atom with a charge Positively charged ion = atom has lost 1+

electron(s) Negatively charged ion = atom has gained 1+

electron(s)11Contreras

Atomic number - # of protons in nucleus

Atomic number (# of protons) is the same for all atoms of a certain element

Atomic number tells you what element it is!

Atomic mass (mass number) = protons + neutrons Atomic mass needs to be rounded

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Atomic mass

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Electron Cloud

Maximum # of

Electrons

1 2

2 8

3 18

4 32

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An element’s atomic number tells where it is on the periodic table

Atomic number = # protons (+)

# protons (+) = # electrons (-) As long as the atom is not an ion

Atomic mass = protons + neutrons

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Isotopes

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Atoms of the same element that have different number of neutrons in their nucleus

Isotopes still have same: Atomic number # protons # electrons Different # neutrons

Named according to the mass number hydrogen-1 and hydrogen-2

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Hydrogen has an atomic number of 1

So Hydrogen has 1 proton

Hydrogen has 2 additional isotopes (H with different number of neutrons) Deuterium (1 proton & 1 neutron) Tritium (1 proton & 2 neutrons)

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To find the number of neutrons: Protons + neutrons = mass number Mass number – atomic number (#

proton) = neutrons

Mass numberof Carbon is 12

Mass number: 12Atomic number: - 6# Neutrons: ~6Contreras

An unstable atom where the nucleus will change and eventually fall apart over time

Will give off energy when they fall apart

Ex. Radon; Uranium Found in nature No stable isotope exists

19http://computershopper.com/shoptalk/Radioactive_Man_Number_One_v_1024.jpg

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Ions have a charge Positive charge if lost an electron ▪ K 1+ has lost an electron

Negative charge if gained an electron▪ Cl 2- has gained two electrons

Isotopes Have same number of protons &

electrons, different number of neutrons

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Name Location Charge

Nucleus Center of atom Positive

Proton Nucleus Positive

Neutron Nucleus None

Electron Electron cloud Negative

electron proton/neutron nucleus atom element

smallest mass biggest mass

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