Mini-Lessons The Atom

Mini-Lesson: Parts of the Atoms

What is an atom made of? Protons Neutrons Electrons 1amu=1.7 * 10-24 g +1 Charge 1 amu (atomic mass unit) 1amu=1.7 * 10-24 g Neutrons 0 (neutral) charge 1amu Electrons -1 Charge Found around the nucleus in an electron cloud Virtually no mass The protons and neutrons are located within the nucleus. It has very little volume but almost all of the mass of the atom so it is VERY dense!

What’s in The Box? Zr is Zirconium Element Symbol Zr is Zirconium Atomic Number- tells the number of protons in one atom of the element Zr has 40 Protons (therefore it also has 40 electrons) Atomic Mass (Mass Number) Tells number of protons and neutrons combined (40 + ? = 91)

Elements And Their Atoms Each element has a unique atomic number The number of protons for an element’s atom is constant and unique The number of electrons will equal the number of protons UNLESS the atom is an ion An element’s atom can have a different number of neutrons Since the mass of an atom depends on the protons and neutrons, the mass of an element can change To find neutrons, subtract the atomic # from the atomic mass

Mini-Lesson: Isotopes and Ions

What is the Charge of an Atom? In a typical atom you will have the same number of protons and electrons, what charge does this give the atom? 0 Charge, or it is neutral!

Can a proton leave an atom?? No If it did you would have a NEW element…more on this later!

Can an electron leave or join an atom?? Yes! This is called an Ion If the atom is missing an electron it will be a Positive Ion. If the atom gains and electron it will be a Negative Ion.

Can the number of neutrons change? Yes! This is called an isotope, it will cause the MASS of the atom to change

For Example… Look at the periodic table and find Carbon What is the atomic number? What is the mass number? “Carbon 12” is the most common form of Carbon But you’ve heard of Carbon 14…That is an isotope of Carbon – it has two more neutrons, adding 2 amu to its mass…but it still has only 6 protons To name an Isotope Element Name – Mass #

Isotope of Different Element Element D has 6 protons and 7 neutrons Element F has 7 protons and 7 neutrons Different Element Element J has 27 protons and 32 neutrons Element L has 27 protons and 33 neutrons Isotope Element T has an atomic number of 20 and an atomic mass of 40. Element Z has an atomic number of 20 and an atomic mass of 41.

Mini-Lesson: Electron Arrangement and Bohr Model

Characteristics of Electrons Extremely small mass Located outside the nucleus Moving at extremely high speeds in a sphere Have specific energy levels LecturePLUS Timberlake

Energy of Electrons When atoms are heated, bright lines appear called line spectra Electrons in atoms arranged in discrete levels. An electron absorbs energy to “jump” to a higher energy level. When an electron falls to a lower energy level, energy is emitted. LecturePLUS Timberlake

Electrons have special rules…. You can’t just shove all of the electrons into the first orbit of an electron. Electrons live in something called shells or energy levels. Only so many can be in any certain shell. The electrons in the outer most shell of any element are called valance electrons. Created by G.Baker www.thesciencequeen.net

Electron Levels (Shells) Contain electrons that are similar in energy and distance from nucleus Low energy electrons are closest to the nucleus Identify by numbers 1, 2, 3, 4, 5, 6….. The first shell (1) is lowest in energy, 2nd level next and so on 1<2<3<4 LecturePLUS Timberlake

Atom Models There are two models of the atoms we will be using in class. Bohr Model Lewis Dot Structure Created by G.Baker www.thesciencequeen.net

Bohr Model The Bohr Model shows all of the particles in the atom. In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P written on them. Neutrons should be blank or have an N. In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e. - + + - Created by G.Baker www.thesciencequeen.net

Nucleus 1st shell 2nd shell 3rd shell Adapted from http://www.sciencespot.net/Media/atomsfam.pdf Created by G.Baker www.thesciencequeen.net

Order of Electron Filling All electrons in the same energy level have similar energy. Shell 1 2 electrons Shell 2 8 electrons Shell 3 18 electrons (8 first, later 10) Order of filling for the first 20 electrons Shell 1 2 3 4 2e 8e 8e 2e LecturePLUS Timberlake

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 Created by G.Baker www.thesciencequeen.net

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) Created by G.Baker www.thesciencequeen.net

Mini-Lesson Forces in the Atom The Fantastic Four!

What Forces Keep an Atom Together What Forces Keep an Atom Together ?   There are four natural forces that are responsible for the behavior of an atom’s particles . . . The Fantastic Four!

Forces In The Atom Gravitational Force Electromagnetic Force Attractive force between all objects in the universe Gravity depends upon mass of and distance between objects… This force is not very strong in the atom Electromagnetic Force Opposites attract; likes repel Protons & electrons Electrons and Nucleus

More Forces in the Atom Strong Force Holds protons and neutrons together to make the nucleus Greater than electromagnetic force between protons (since the protons would repel each other) Weak Force – Yes, it’s a very weak force Deals more with radioactive decay and nuclear fusion Weak forces are important because they are responsible for stabilizing particles through the process of radioactive decay, in which a neutron in the nucleus changes into a proton and electron.

Mini-Lesson Groups, Periods, and The Lewis Dot Structure

Lewis Dot Structure O •• • • • • The Lewis Dot Structure is a bit different from the Bohr model. It only shows the element symbol and it’s outer most electron shell, the valence electrons. + - •• O • • • • Created by G.Baker www.thesciencequeen.net

The Periodic Table Columns are called groups or families, and as family members, they have similar properties Rows are called periods. They do not share properties, but properties change as one goes from left to right

The Periodic Table

The first element in a period is always an extremely active solid. The last element in a period is always a particularly inactive gas. These are referred to as the “noble gases.”