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Chapter 2 Atoms and Elements. Electron Arrangement and Periodic Law. Characteristics of Electrons. Extremely small mass Located outside the nucleus Moving at extremely high speeds in a sphere Have specific energy levels. Energy of Electrons.

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chapter 2 atoms and elements
Chapter 2Atoms and Elements

Electron Arrangement and Periodic Law

LecturePLUS Timberlake

characteristics of electrons
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
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

loss and gain of energy
Loss and Gain of Energy

Loss

G

a

I

n

LecturePLUS Timberlake

learning check ea1
Learning Check EA1

Answer with

1) Energy absorbed 2) Energy emitted

3) No change in energy

A. What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?

B. What energy change takes place when the electron moves from the third shell to the second shell?

LecturePLUS Timberlake

solution ea1
Solution EA1

A. 1) Energy absorbed

B. 2) Energy emitted

LecturePLUS Timberlake

bohr model
Bohr Model
  • First model of the electron structure
  • Gives levels where an electron is most likely to be found
  • Incorrect today, but a key in understanding the atom

LecturePLUS Timberlake

quantum mechanics
Quantum Mechanics

Describes the arrangement and space occupied by electrons in atoms

LecturePLUS Timberlake

electron levels shells
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

number of electrons
Number of Electrons

Maximum number of electrons in any electron level = 2n2

n =1 2(1)2 = 2

n =2 2(2)2 = 8

n =3 2(3)2 = 18

LecturePLUS Timberlake

order of electron filling
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

electron configuration
Electron Configuration
  • Lists the shells containing electrons
  • Written in order of increasing energy

Element Shell 1 2 3

He 2

C 2 4

F 2 7

Ne 2 8

Al 2 8 3

Cl 2 8 7

LecturePLUS Timberlake

learning check ea2
Learning Check EA2

A. The electron configuration for sulfur

1) 2,6 2) 8,2,6 3) 2, 8, 6

B. The element in period 3 with two electrons in the outermost energy level

1) Mg 2) Ca 3) Be

LecturePLUS Timberlake

solution ea2
Solution EA2

A. The electron configuration for sulfur

3) 2, 8, 6

B. The element in period 3 with two electrons in the outermost energy level

1) Mg

LecturePLUS Timberlake

learning check ea3
Learning Check EA3

Indicate the number of electrons in the final notation of the electron configuration for each:

A. O 1) 4 2) 6 3) 8

B. Al 1) 13 2) 3 3) 1

C. Cl 1) 2 2) 5 3) 7

LecturePLUS Timberlake

solution ea3
Solution EA3

Indicate the number of electrons in the final notation of the electron configuration for each:

A. O 2) 6

B. Al 2) 3

C. Cl 3) 7

LecturePLUS Timberlake

learning check ea4
Learning Check EA4

For phosphorus, indicate if each configuration is (1) correct or (2) incorrect. Explain why or why not?

A. 2, 2, 8, 5 1 or 2

B. 2, 8, 3 1 or 2

C. 2, 8, 5 1 or 2

D. 2, 6, 7 1 or 2

LecturePLUS Timberlake

solution ea4
Solution EA4

For phosphorus, indicate if each configuration is (1) correct or (2) incorrect. Explain why or why not?

A. 2, 2, 8, 5 2Shell 2 holds 8e-

B. 2, 8, 3 2 P has 15 electrons

C. 2, 8, 5 1Correct arrangement

D. 2, 6, 7 2Shell 2 holds 8e-

LecturePLUS Timberlake

periodic law
Periodic Law

All the elements in a group have the same electron configuration in their outermost shells

Example: Group 2

Be 2, 2

Mg 2, 8, 2

Ca 2, 2, 8, 2

LecturePLUS Timberlake

learning check ea5
Learning Check EA5

Specify if each pair has chemical properties that are similar (1) or not similar (2):

A. Cl and Br

B. 2 - 5 and 2 - 8 - 7

C. 2 - 4 and 2 - 8 - 4

D. P and S

E. O and S

LecturePLUS Timberlake

solution ea5
Solution EA5

Specify if each pair has chemical properties that are similar (1) or not similar (2):

A. Cl and Br 1

B. 2 - 5 and 2 - 8 - 7 2

C. 2 - 4 and 2 - 8 - 4 1

D. P and S 2

E. O and S 1

LecturePLUS Timberlake