Atoms, Isotopes, and Bohr!

What makes up an atom?1. An atom is made up of subatomic

particles (protons, neutrons, and electrons.) Protons and neutrons are made up of Quarks.

2. An element is made up the same type of atom.

Parts of the Atom

Proton Electron

Neutron

What do you notice about the size of each type of particle?

What does an atom really look like? An atom has a very dense center called a nucleus where the protons and neutrons are located. The electron cloud is the space around the nucleus. The dots show where an electron is likely to be.

Parts of the Atom

Charge Mass (amu) Location

Proton + 1 1 (very large!) nucleus

Neutron 0 1 (very large!) nucleus

Electron - 1 .0005 (very very small!) outside nucleus

What holds an atom together? Because protons have a positive charge and electrons have a negative charge, they are attracted to each other because of the electromagnetic force (opposite charges attract, like charges repel.)

Atom Diagrams1. We diagram an atom with electrons

moving in electron shells around the nucleus.

2. The farther away the electron is from the nucleus, the more energythe electron has.

3. Electrons in energy levels are grouped in pairs.

Let’s Review

1. What does the atomic number tell you?

1. How do you find the number of neutrons?

Bohr Model Electron Shells

Bohr Model Practice

So let’s try it….How to draw a Lithium atom

First, look at the Periodic Table

Second, determine the number of protons (Look @ the atomic number)

Then determine the number of neutrons (Atomic mass – atomic number)

Then determine the number of electrons (Look @ the atomic number)

3

LiLithium

7

So let’s try it….3

LiLithium

7

+

++

Protons = 3

Neutrons = 4

(7-3=4)

-

-

-

Electrons = 3 2 in the 1st shell, 1 in the 2nd shell

Isotopes- An isotope is an atom that has the same number of protons, but a

different number of neutrons.

Isotopes (continued)- You can think of isotopes like atoms having a twin or triplet. It is the

same element, just a different version of it.

- The element doesn’t change because they have the same atomic number

How can you tell one isotope from another? - Although isotopes share most of the

same physical and chemical properties, Isotopes of the same element have different mass numbers.

- Atomic Mass = protons + neutrons

- Protons and Neutrons have a mass of about 1 atomic mass unit (amu)

- Electrons have such a small mass they are considered to be 0 amu

Parts of the Atom

Charge Mass (amu) Location

Proton + 1 1 (very large!) nucleus

Neutron 0 1 (very large!) nucleus

Electron - 1 .0005 (very very small!) outside nucleus

What’s the difference? Why are they different? Atomic Mass

- The total mass of one atom of an element

- Because elements have isotopes, the atomic mass listed on the periodic table is a weighted average of all the naturally occurring isotopes of an element.

Atomic Mass and IsotopesThere is a lot more Hydrogen-1 than Hydrogen-2 so Hydrogen-1 is weighted more heavily when calculating the atomic mass of hydrogen.

Mass: ______ Mass: ______ Mass: ______