Atoms, Isotopes, and Bohr!

What makes up an atom? An atom is made up of subatomic particles (protons, neutrons, and electrons.) Protons and neutrons are made up of Quarks. An element is made up the same type of atom.

Parts of the Atom Neutron Proton Electron What do you notice about the size of each type of particle? Proton Electron

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 Electron - 1 .0005 (very very small!) outside nucleus Parts of the Atom

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 Diagrams We diagram an atom with electrons moving in electron shells around the nucleus. The farther away the electron is from the nucleus, the more energy the electron has. Electrons in energy levels are grouped in pairs.

Let’s Review What does the atomic number tell you? How do you find the number of neutrons?

Bohr Model Electron Shells

Bohr Model Practice

So let’s try it…. Li Lithium 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 Li Lithium 7

So let’s try it…. Li Lithium Protons = 3 3 7 Neutrons = 4 (7-3=4) - + Electrons = 3 2 in the 1st shell, 1 in the 2nd shell Neutrons = 4 (7-3=4)

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 Electron - 1 .0005 (very very small!) outside nucleus Parts of the Atom

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 Isotopes There 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: ______