chapter 2 matter is made of atoms 2.2 electrons in atoms

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

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Page 1: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Chapter 2 Matter is Made Chapter 2 Matter is Made of Atomsof Atoms2.2 Electrons in Atoms

Page 2: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

ObjectiveObjective

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

Page 3: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electrons in motionElectrons in motionElectrons are in motion in the

outer part of an atomWhen two atoms come near,

these electrons interactElectrons and their arrangement

in the atom greatly affect an element’s properties and behavior

Page 4: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electrons in motionElectrons in motionNiels 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.

Page 5: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic 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

Page 6: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrum

Electromagnetic waves travel through space at the speed of light, approx. 300 million meters/sec

Page 7: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrumProperties 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 frequencyLow frequency = long wavelength (low energy)High frequency = short wavelength (high

energy)

Page 8: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrum

Page 9: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrumAll 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

Page 10: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrum

Page 11: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrumGamma 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

Page 12: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrumVisible- part of the spectrum to

which our eyes are sensitive, Our eyes and brains interpret different frequencies as different colors

ROY G BIV - NewtonRed- low energy

Violet- high energy

Page 13: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electromagnetic spectrumElectromagnetic spectrumInfrared- less energy than visible,

given off by most “warm objects”

Microwaves/ Radio waves- lowest frequency

Page 14: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electrons and LightElectrons 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)

Page 15: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

Electrons and LightElectrons and LightENERGY 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 electronshttp://www.youtube.com/watch?v=QI50GBUJ48s&safety_mode=true&persist_safety_mode=1&safe=active

Page 16: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

# of electrons in each # of electrons in each levellevelLowest 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

Page 17: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

# of electrons in each # of electrons in each levellevelBohr 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)

Page 18: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

VALENCE ELECTRONSVALENCE ELECTRONSThe 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.)

Page 19: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

VALENCE ELECTRONSVALENCE ELECTRONSAtoms in group 1 have one valence electronAtoms in group 2 have two valence electronsAtoms in group 13 have three valence

electronsAtoms in group 14 have four valence electronsAtoms in group 15 have five valence electronsAtoms in group 16 have six valence electronsAtoms in group 17 have seven valence

electronsAtoms in group 18 have eight valence

electrons

Page 20: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

LEWIS DOT DIAGRAMLEWIS 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  

Page 21: Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

LEWIS DOT DIAGRAMLEWIS DOT DIAGRAMLi 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