1. I love science, Ms. Solari!
What is an atom?
I love science, Ms. Solari!
No, not this
kind of Adam!

2. What is an atom? All matter in the universe is made up of atoms.
An atom is the smallest particle of an element that has all the properties of that element.
Parts of the Atom— Subatomic Particles
Nucleus—small, dense, positively charged center of the atom. It contains most of the atom’s mass. Protons and neutrons are located in the nucleus.
Proton—has a positive (+) charge
Neutron—has no charge (neutral)
Electron Cloud— area surrounding the nucleus where the electrons are found. An electron is very small a negatively (-) charged particle moving very quickly in the area around the nucleus.
The atom is mostly empty space.

3. Subatomic particle Location Charge Relative mass (amu)
Subatomic Particles: Most atoms are composed of 3 major subatomic particles
Subatomic particle
Location
Charge
Relative mass (amu)
Proton
Nucleus
Positive (+)
1 amu
Neutron
Neutral (n)
Electron
Electron cloud
Negative (-)
1/2000 amu

4. All atoms of the same element have the same chemical and physical properties as one another.
When an atom has the same number of protons (+) and electrons (-), the atom is neutral (has no electric charge). When atoms gain or lose electrons, they become charged atoms or ions.

5. Properties of an Atom
Each element is represented by a box on the periodic table. The box gives information about the atoms of that element. All of the atoms of a certain element are alike. The atoms of different elements are different.
2 atomic number
He chemical symbol
(Helium) element name
atomic mass

6. Properties of an Atom
Chemical Symbol—every element has its own symbol. The first letter is always capitalized. The second letter, if there is one, is always a lower case letter.
Atomic number describes the number of protons (+) in each atom of an element. Every element has a unique atomic number. In a neutral atom, the number of protons equals the number of electrons.
Atomic mass is the average mass of the atoms of an element often expressed in atomic mass units (amu); atomic mass is sometimes referred to as the atomic weight.

7. The number of protons and neutrons may be different.
Mass Number is the total number (the sum) of the protons and neutrons in the nucleus of an atom.
The number of protons and neutrons may be different.
To find the mass number, round the average atomic mass to get an approximate mass number. Subtract the number of protons (atomic number) from the mass number to get the number of neutrons.
Use your periodic table to complete the following chart.
Element name
Symbol
Atomic #
Atomic mass
Mass #
# of protons
# of neutrons
# of electrons
Calcium 40 20 B 5 10
20.180
Chlorine Cl

8. Isotope is the atom of an element that has a different number of neutrons from other atoms of that element. It still has the same number of protons.
Example:
A common carbon atom has a mass number of 12 (6 protons and 6 neutrons) and may be written as C-12. An isotope of carbon with a mass number of 14 has 6 protons and 8 neutrons (it is heavier) and may be written as C-14. Carbon-14 has 2 extra neutrons but still has the same number of protons and electrons as C-12. C-14 is an isotope of C-12.
Hydrogen is the smallest atom. Most atoms of Hydrogen have 1 proton and 0 neutrons.
H-1 has ____________________ neutrons.
H-2 has ____________________ neutrons.
H-3 has ____________________ neutrons.

9. Models of the Atom
The Electron Cloud Model (Quantum Mechanics)—Modern Theory
Because electrons move so fast, they appear to be in many places at the same time. This causes a “blur” around the nucleus called the “electron cloud”
This model represents the most likely area for an electron to be found
Most accurate theory to date

10. The Bohr Model of an Atom
Neils Bohr was a Danish scientist who said that electrons move around the nucleus in certain paths or energy levels much the same as the planets orbit the sun. His model is sometimes called the “planetary” model.
Sample Bohr Model
3rd energy level
(outermost)
2nd energy level
1st energy level
nucleus

11. The Bohr Model:
A clear and easy model of the atom, but not accurate
Electrons are shown in energy levels which are defined paths around the nucleus
The energy levels are in circular paths around the nucleus.
Each energy level can “hold” a certain number of electrons before it is “full”
For the first 18 elements found on periodic table:
1st level—2 electrons
2nd level—8 electrons
3rd level—8 electrons
The electrons in the outermost energy level are called valence electrons; they determine the chemical reactivity of the atom. Chemical reactivity refers to how each element will react or bond with another element or molecule.

12. The outer energy level or “shell” is considered full when it has the maximum number of electrons that can fit into that level (for example, the 1st level is full when it has 2 electrons, but the 2nd and 3rd levels are full when it has 8 electrons.)
If the outside energy level is full, it is considered non-reactive. It does not need to chemically react or bond with any other atom or molecule.
If the outside energy level is incomplete (not full), it is considered reactive. It will either lose or gain electrons and chemically react or bond with another atom or molecule.
Electrons can move from one energy level to the next (if it gains or loses energy)
Electrons closest to the nucleus have the lowest amount of energy

13. Reactive Non-reactive Reactive & Isotope
Sample Bohr Models O Ne Be