1. The Atom & Chemical Bonds
Packet #5
Chapter #2

2. Introduction to Atoms & Elements
The smallest particle of an element
Elements are composed of atoms
Element
A substance composed of atoms having an identical number of protons in each nucleus.
A substance that cannot be decomposed into simpler substances
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3. A Closer Look at the Atom
Two “broad” regions
Interior & Exterior
Interior Region is called the Nucleus
Protons
Have a positive charge
Neutrons
Have a neutral charge (no charge)
Exterior Region is called the Electron Shell/Cloud
Electrons
Negative charge
Surround the atom
Used in the formation of chemical bonds
Valence Electrons
Helps determine what type of bonds are made
Helps determine how many bonds are made
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4. The Helium Atom

5. The Periodic Chart The Periodic Chart
Is a list of all elements, but more importantly, it lists the characteristics of the atoms that make up each element.
The list provides the number of protons, the atomic number, and the atomic mass of the atom found within a particular element.
Hydrogen is the lightest of all elements and is a colorless and a highly flammable gas

6. The Periodic Chart & Elements The Equation
The Periodic Chart shows the atomic number and atomic mass of the elements
Atomic Number (Z)
The number of protons in the nucleus of an atom
Atomic Mass (A)
The absolute atomic mass of an atom
Equation
A = Z + N
N = number of neutrons in the nucleus of an atom
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7. Question
If the atomic mass of an element is 29, and the number of neutrons is 15, what element am I talking about?
A = Z + N
29 = Z + 15
Z =
Z = 14
What element has an atomic number of 14?
Si (Silicon)
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8. Models that Represent the Atom
The Bohr Model
Models that Represent the Atom

9. Introduction I
The Bohr Model is the simplest modern picture of the structure of the atom.
Developed by Danish physicist Niels Bohr
Shows
The number of protons and neutrons located within the nucleus of the atom.
The electrons spinning within the exterior region in specified areas known as shells.

10. Electrons & Shells
Electrons spin within specified regions called shells.
However, it must be noted that shells are composed of separate regions known as orbitals
More to come later.
Each shell holds a specified maximum number of electrons
1st Energy Level
2 electrons
2nd Energy Level
8 electrons
3rd Energy Level
18 electrons
**8 electrons for elements found in row #3 only
4th Energy Level/Shell
32 electrons
Examples of Carbon, Oxygen and Nitrogen
Bohr Model
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11. Electrons in the Most Outer Shell
Electrons found in the most outer shell are called valence electrons
These electrons are used in the formation of chemical bonds
Valence
Not the same as valence electrons
The number of electrons required to fill the most outer shell

12. Movement of Electrons from Shell to Shell

13. Movement of Electrons Between Shells I
Electrons have the capability of moving
When electrons move from a low energy level to one that is higher, energy is absorbed.
Exergonic reaction
Requires the input of energy
Endothermic reaction
Reaction that absorbs energy in the form of heat
When electrons move from a high energy level to one that is lower, energy is lost.
Endergonic reaction
Energy is lost
Exothermic reaction
Reaction that releases energy in the form of heat

14. Isotopes

15. Isotopes One of two or more atoms with very similar properties.
However, the atomic mass is different.
The atomic number remains the same.
In order to change the atomic mass, if the atomic number is the same, then the number of neutrons must be changed.
Examples

16. Electron Shells & Orbitals

17. Orbitals & Electron Configuration
Describes the volume of space around a nucleus in which the electron is most likely to be found
There are four different types of orbitals that have the ability to hold a different maximum amount of electrons
S = 2
P = 6
D = 10
F = 14
Important to remember that orbitals make up shells

18. Orbital & Shell Connection
Recall
Orbitals are represented by letters
See last slide
Shells will be represented by numbers that hold different maximum numbers of electrons
1st shell = 2 electrons
2nd shell = 8 electrons
3rd shell = 18 electrons (8 for elements in the 3rd row)
4th shell = 32 electrons
How are those numbers calculated?
Illustration on board

19. Representing Orbitals
Orbitals, surrounding different atoms, are represented in a form known as the electron configuration.
Illustration of electron configuration on the board
Carbon
Oxygen
Nitrogen
Hydrogen