Atomic structure and periodicity

Question 1

The behaviors of the verysmall

Answer 1

Electrons are incredibly small

Electrons behavior determines much of the behavior of atoms

Directly observing electrons in the atom is impossible; the electron is so small that observing it changes its behavior

Question 2

Why Quantium mechanics?

Answer 2

Classical mechanics (Newton’s mechanics) and Maxwell’s equations (electromagnetic theory) can explain MACROSCOPIC phenomena such as motion of balls rockets

Until the beginning of the 20th century it was believed that all physical phenomena were deterministic (definite, predictable future)

Question 3

The beginning of quantum mechanics

Answer 3

Quantum mechanics: used to explain microscopic phenomena such as photon-atom scattering and flow of the electrons in a semiconductor

Work done at that time by many famous physicists discovered that for sub-atomic particles, the present condition does not determine the future conditions

Question 4

What is the best tool for studying the structure of atoms?

Answer 4

Electromagnetic radiation

One of the ways energy travels through space is through electromagnetic radiation

What we call light, is just one form of electromagnetic radiation

It is importantly to know the properties of light in order to understand how atomic structure is revealed by electromagnetic radiation

Question 5

Wavelength

Answer 5

The distance between two successive rests

Units: meters or nanometers

Question 6

Frequency

Answer 6

The number of waves passing a certain point over a unit of time

Units: s^-1 = Hz

Question 7

Amplitude

Answer 7

Height of the wave measured from the axis of propagation, a measure of intensity

Question 9

Equation

Answer 9

c = hv

h = c/v

v = c/h

Question 10

Color

Answer 10

The color of light is determined by its wavelength or frequency

White light is a mixture of all the colors of visible light

A spectrum
Red, orange, yellow, green, blue, indigo, violet

Question 11

Interference in two overlapping light waves

Answer 11

When two or more waves meet the can interact (interfere) either constructively or destructively

Question 12

Diffraction

Answer 12

Before the 19th century very little was known about the nature of light and one the great debates about light was over the question of whether light was made of a bunch of “light particles” or whether light was a wave

When traveling waves encounter a obstacle of opening in a barrier that is about the same size as the wavelength, they bend around it—this is called diffraction

Question 13

Young’s double-slit experiment

Answer 13

Around 1800, Thomas Young settled the question by performing an experiment in which he shone light through very narrow slits and observed the results

Question 14

Refraction of light

Answer 14

As the light passes from one medium to another it’s speed changes, causing the light to bend

Question 15

Quantum theory

Answer 15

The nature of energy

The wave of nature of light does not explain how an object can glow when its temperature increases

Question 16

The nature of energy and matter

Answer 16

In 1900, Planck found that if light can only be emitted in small bursts, rather than continuous wave, the resulting calculation matched what people measured experimentally

Postulated that energy can be gained or lost only in whipped number multiples of the quantity: hv

h (planck’s constant): 6.626 x 10^-34

The change in energy for a system
E = nhv

n = integer, v = frequency

Question 17

The photoelectric effect

Answer 17

Heinrich Hertz, 1888
Light sticking the surface of certain metals causes ejection of electrons

Below a certain frequency, no electrons were observed, no matter what the intensity

The energy of the ejected electrons increases linearly with the frequency of light

The number of emitted electrons increased with light intensity

All metals show the same pattern, but each metal has a different threshold frequency

Question 18

Einstein’s explanation

Answer 18

Postulated that if one assumes that light is made up particles

Light has two properties
Wave-like
Particle-like

The “particles” are called photons, which are packets of energy

A high energy photon (particle) bumps into an atom, ejecting an electron

Question 19

Is light a wave or a flow of particles?

Answer 19

It’s neither one. Light is a “quantum vector field”

This multiple personality of light is referred to as “wave-particle duality”

Light behaves as a wave or as particles, depending on what we do with it, and what we try to observe

Its wave-particle duality that lies at the heart of the Heisenberg uncertainty

Question 20

Equation for photoelectric effect

Answer 20

1/2 mu^2

m = mass
u = speed

At frequencies greater than v0:

Vs = k(v-v0)

Ek = Ephoton - Ebinding

Question 21

Atomic spectra

Answer 21

For atoms and molecules one does not observe a continuous spectrum, one gets from a white light source

Only a line spectrum of discrete wavelengths is observed

Question 22

Rydberg’s spectrum analysis

Answer 22

Analyzed the spectrum of hydrogen and found that it could be described with an equation that involved an inverse square of integers

1/h = -R( 1/n^2 —1/n^2)

R = 1.096776 x 10^7 m^-1

Question 23

Rutherford nuclear model

Answer 23

The atom contains a tiny dense center called the nucleus

The nucleus is essentially the entire mass of the atom

Positively charged

The electrons move around in the empty space of the atom surrounding the nucleus

Question 24

Problems with Rutherford’S nuclear model

Answer 24

Elections are moving charged particles

Moving particles give off energy

Electrons should lose energy, crash into the nucleus and the atom should collapse

But it doesn’t

Question 25

The Bohr atom

Answer 25

Niels Bohr adopted planck’s assumption and explained these phenomena in this way:

1. Electrons in an atom can only occupy certain orbits
2. Electrons in permitted orbits gave specific , “ allowed” energies; these energies will not be radiated from the atom
3. Energy is only absorbed or emitted in such a way as to move an electron from one “allowed” energy state to another; the energy is defined by E = hv

En = -RH/n^2

Question 26

Energy level diagram for the hydrogen atom

Answer 26

The energy absorbed or emitted from the process of electron promotion or demolition can be calculated by the equation:

E= -RH (1/n^2 —1/n^2)

Ephoton = hv =. hc/

Rh = 2.18 x 10^-18 J