Structure of Atoms

• Atom: basic unit of matter
• Structure:
• Nucleus: center of the atom. Contains Protons (+) & Neutrons (o)
• Electrons (-) : orbit the nucleus according to energy levels
• Level 1: 2 electrons
• Level 2: 8 electrons
• Level 3: 18 electrons
• Every element has a unique # of protons.

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Structure / Periodic Table

• Atomic number = represents the # of protons
• Ex: Oxygen = 8 protons

Hydrogen = 1 proton

Magnesium = 12 protons

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• Mass of one individual atom = total # of P and N
• Ex: Oxygen = 8 protons + 8 neutrons = 16

Oxygen = 8 protons + 9 neutrons = 17

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Magnesium = 12 protons + 10 neutrons = 22

Magnesium = 12 protons + 12 = 24

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• Mass on Periodic Table = average of all the isotopes
• Ex: Oxygen = average of all isotopes is 15.999

Hydrogen = average of all isotopes is 1.0078

Magnesium = average of all isotopes is 24.305

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DON’T USE THE MASS ON THE PERIODIC TABLE

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• Charge: atoms with more or less electrons than protons
• Ex: Oxygen - 8 protons & 7 electrons = +1 charge

Oxygen - 8 protons & 9 electrons = -1 charge

Oxygen - 8 protons & 10 electrons = -2 charge

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Practice!!!

• Use your periodic table to fill out the practice questions!
• Pay attention to what the question is asking for.
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Different Types of Elements

• IONS: elements with a net CHARGE due to the LOSS or GAIN of ELECTRONS.
• Protons: STAY THE SAME
• Neutrons: STAY THE SAME
• Electrons: MAY GO UP OR DOWN IN NUMBER (creates a charge)

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• What does the number or symbol next to the element’s symbol represent?

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The charge of the atom (- or +)

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Different Types of Elements

• ISOTOPES: Elements that have multiple forms.
• Protons: STAY THE SAME
• Neutrons: EQUAL TO PROTON # OR LARGER (more neutrons help stabilize the nucleus)
• Different atomic MASS but still the same ELEMENT

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