Atomic Structure

Modern Atomic Theory:1. All matter is made of atoms, too small to see.

2. Each element has its own kind of atom. Atoms of the same element have same mass. Atoms of different elements have different masses.

3. Compounds are formed when atoms of different elements link to form molecules or ionic compounds.

4. Atoms cannot be created or destroyed in physical or chemical reactions.

What are the 3 major parts of an atom?

• Proton (+)

• Neutron (no charge)

• Electron (-)

Where is everything located?

Protons and Neutrons are found in the nucleus (the central part of the atom)

Electrons orbit the nucleus.

The Proton

• Protons are positively charged particles found in the atomic nucleus.

• Protons were discovered by Ernest Rutherford.

The Neutron

• Neutrons are uncharged particles found in the atomic nucleus.

• They were discovered by James Chadwick in 1932

The Electron

• Electrons are negatively charged particles that surround the atom's nucleus.

• Electrons were discovered by J. J. Thomson in 1897.

• Electrons determine properties of the atom.

• Chemical reactions involve sharing or exchanging electrons.

The Nucleus

• The nucleus is the central part of an atom. It is composed of protons and neutrons.

• The nucleus contains most of an atom's mass

• It was discovered by Ernest Rutherford in 1911.

What is the Electron Cloud Model?

Model of the atom pictures the electrons moving around the nucleus in a region called an electron cloud.

The electron cloud is a cloud of varying density surrounding the nucleus. The varying density shows where an electron is more or less likely to be (its always moving so we cant pinpoint it!)

Calculating #’s of e-, p+ and no

• For Krypton:– # protons = atomic number = 36– # electrons = # protons (neutral) = 36– # neutrons = Atomic Mass – Atomic Number

= 84 – 36 = 48

Can find the information in any order…

• Atomic Number = 78

• Atomic Mass = 195

• How many electrons, protons and neutrons and what is it?– #protons = 78 = # electrons– # neutrons = 195 – 78 = 117– What is it?? Pt (Platinum)

Ions

• The number of electrons doesn’t always equal the number of protons … if you have an ion!!

• It’s not neutral, but has an overall charge

Charges

• POSITIVE - The element LOSES electrons from the neural atom

• NEGATIVE – The element GAINS electrons from the neutral atom

• The magnitude of the charge tells you how many electrons are lost/gained

O2-

• Oxygen has an atomic number of 8– # protons = 8 (ALWAYS the same as Atomic

number)– # electrons = 2 more than neutral = 10– # neutrons = 16 – 8 = 8

K+

• Atomic Number = 19 = # protons

• Positive 1 = Loses one electron = 18

• # neutrons = 39-19 = 20

IsotopesIsotopes: Different forms of the SAME element based on the number of NEUTRONS in

the nucleus.

Therefore, the isotope will have a different mass than the naturally occurring form of the element (different than what the periodic table tells us).