1. Chapter 2 Matter is Made of Atoms
2.2 Electrons in Atoms

2. Objective
Objectives: Relate the electron to modern atomic theory, Compare electron energy levels in an atom, Illustrate valence electrons by Lewis electron dot structures

3. Electrons in motion
Electrons are in motion in the outer part of an atom
When two atoms come near, these electrons interact
Electrons and their arrangement in the atom greatly affect an element’s properties and behavior

4. Electrons in motion
Niels Bohr (early 20th century)- Proposed e-‘s must have enough energy to keep them in constant motion around the nucleus (enables e-‘s to overcome the attraction of the positive nucleus)
Bohr’s model (1913)- Planetary model
The well-defined orbits are not correct. Electron motion within an atom is irregular and an electron may be close to the nucleus at times.

5. Electromagnetic spectrum
Electromagnetic radiation (radiant energy) travels in the form of waves- have both electrical and magnetic properties
Electromagnetic waves can travel through empty space
Ex: radiant energy from the sun travels to Earth

6. Electromagnetic spectrum
Electromagnetic waves travel through space at the speed of light, approx million meters/sec

7. Electromagnetic spectrum
Properties of waves: Frequency and wavelength
Frequency-number of vibrations/ second (Hertz-Hz)
Wavelength- distance between two corresponding points on two consecutive waves
Wavelength is determined by frequency
Low frequency = long wavelength (low energy)
High frequency = short wavelength (high energy)

8. Electromagnetic spectrum

9. Electromagnetic spectrum
All the forms of radiant energy are parts of a whole range of electromagnetic radiation
The electromagnetic spectrum includes gamma rays, X rays, ultraviolet (UV), Visible, Infrared (IR), microwaves, radio waves

10. Electromagnetic spectrum

11. Electromagnetic spectrum
Gamma Rays- highest frequency, shortest wavelength, most energetic waves, can pass through most substances
X rays- lower frequency than gamma, but still high energy waves, can pass through soft body tissue, but stopped by bone
Ultraviolet-slightly more energetic than visible, can cause sunburns, mostly absorbed by ozone

12. Electromagnetic spectrum
Visible- part of the spectrum to which our eyes are sensitive, Our eyes and brains interpret different frequencies as different colors
ROY G BIV - Newton
Red- low energy
Violet- high energy

13. Electromagnetic spectrum
Infrared- less energy than visible, given off by most “warm objects”
Microwaves/ Radio waves- lowest frequency

14. Electrons and Light
EMISSION SPECTRUM: Spectrum of light released from excited atoms of an element
Electrons can have only certain amounts of energy
Electrons can move around the nucleus only at distances that correspond to those amounts of energy
When e- absorb energy, they move to a higher energy state
When they fall back to a lower energy state- they emit energy (Light)

15. Electrons and Light
ENERGY LEVEL: Region of space in which e-‘s can move about the nucleus of an atom
ELECTRON CLOUD: Space around the nucleus of an atom where the atom’s e-‘s are found
Each energy level can hold a limited number of electrons
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16. # of electrons in each level
Lowest energy level is the smallest and closest to the nucleus, Holds two electrons max
Second energy level is larger because it is farther away, Holds eight electrons max
Max # of e-‘s: 2, 8, 8,18, 32, 50, 78, 91

17. # of electrons in each level
Bohr Model Examples:
H-1 (1 p, 1 e, 0 n)
Li-7 (3 p, 3 e, 4 n)
0-16 (8 p, 8 n, 8 e)

18. VALENCE ELECTRONS The electrons in the outermost energy level
Valence electrons are important because they interact when atoms come near each other
Chemical and physical properties of an element are directly related to the number and arrangement of valence electrons (v.e.)

19. VALENCE ELECTRONS Atoms in group 1 have one valence electron
Atoms in group 2 have two valence electrons
Atoms in group 13 have three valence electrons
Atoms in group 14 have four valence electrons
Atoms in group 15 have five valence electrons
Atoms in group 16 have six valence electrons
Atoms in group 17 have seven valence electrons
Atoms in group 18 have eight valence electrons

20. LEWIS DOT DIAGRAM
Illustrates valence electrons as dots around the chemical symbol of an element.
Each dot represents one valence electron (max # of v.e. is 8)
The symbol represents the core of the atom Ex:
Li  Be   B 

21. LEWIS DOT DIAGRAM
Li has 2 e- in the first energy level and 1 in the second,
Be has 2 e- in the first energy level and 2 in the second,
B has 2 e- in the first energy level and 3 in the second
More examples: C, N, O, F, Ne