Chapter 4 - Subatomic Particles

what is a Physical model

a scale model of something either too big or too small to study in its regular size

examples of physical models include

buildings; bacteria

what is a conceptual model

a model used to describe a system, something that does not have a regular shape

what are examples of conceptual models

atoms, weather

what was the first subatomic particle discovered

the electron

explain the Cathode Ray Tube

applying a voltage across a sealed tube of gas produces a particle beam

what is an example of a cathode ray tube

a television

if particles are drawn towards a positive place they must be

negatively charged

electrons are noted as having a what kind of charge

a negative one (-1) charge

compared to the mass of a hydrogen atom, electrons are very light-

about 1/2000th of the weight of a hydrogen atom

J J Thompson invented the

plum pudding model (atomic model)

the plum pudding (atomic) model answers these questions:

something must neutralize the negative charge of the electron; how to combine both charges

Ernest Rutherford proved

the plum pudding model in 1909

Ernest Rutherford designed an experiment using positively charged

a- particles (He nucleus) with high speed

the expected result of rutherford’s experiment was that the a-particles would pass through the

gold foil virtually undisturbed

the experimental results of rutherford’s experiment were that the majority of particles

passed through without deflection (1 in 20,000 bounced back)

the conclusion of rutherford’s atomic model experiment were that atoms

must be mostly empty space with a massive, positively charged nucleus

the nucleus is made up of

protons and neutrons

protons have a charge of

plus 1 (+1)

neutrons (also called nucleons) have what charge?

no charge; 0 charge

both protons and neutrons weigh about the same and are

2,000 times heavier than an electron (or about the weight of a hydrogen atom)

mass number is the number of

neutrons (nucleons) in an atom

atoms of the same element always have the same atomic number but

the mass number may vary

mass number equation

proton plus neutron

atomic number is the

number of protons

isotopes are atoms of the same element that have

different mass numbers

what is the unit used to measure the atomic mass or actual mass of an atom

amu or atomic mass unit

1 amu =

1/12 the mass of 12 carbon atoms

the weighted average atomic mass is the

average atomic mass of isotopes according to their natural abundance

to find the average atomic mass of isotopes according to their natural abundance, you would use the equation

(mass of isotope 1 x abundance of isotope 1) + (mass of isotope 2 x abundance of isotope 2) + …

natural atoms must have the following relationship

the number of electrons must equal the number of protons (#p = #e)

number of protons tells you what element

you are dealing with

if the proton number has changed then the

element has changed

number of protons affects the

mass number

number of electrons affects the

charge of the atom

elements can be charged if

they gain or lose electrons (noted by a + or - sign in the upper right hand corner)

positive ions are

cations (Ca2+, Na+, Fe+3)

negative ions are

anions (N3-, Cl-)

light is a form of energy we call

electromagnetic radiation

wavelength is the distance from

crest to crest or troth to troth in an electromagnetic wave

a shorter wavelength means there is

more / higher energy

a longer wavelength means there is

less / lower energy

wave frequency tells is how fast

the waves are oscillating (Hz)

high frequency / short wavelength means there is

a lot of energy

low frequency / longer wavelengths mean there is

not a lot of energy

white light is

all visible light waves together

each color has its own different

frequency

a spectroscope is an instrument used to observe the

color components of light

for white light you see all the colors in a

continuous band

light from an atom is

not a continuous band

when atoms are excited by electricity or heat, they emit

discrete bands of color

each element emits a unique band of colors, similar to how every person has

a unique fingerprint

light and mass are

quantized

quantum is a

distinct packet of energy

one quantum of light is called

a photon

light acts as both

a wave and a particle

when referring to light as a particle we are talking

about photons

it is these light particles (photons) that interact

with electrons

electrons orbit around

the nucleus

the bohr model resembles a

solar system with the sun as the nucleus and each planet as the electron

the bohr model is also known as

the planetary model

each orbit has a

quantum number (n=1, n=2)

the higher the quantum number, the

farther away the electron is from the nucleus

can there be an n=1.5 orbit?

no, electrons can only be in orbits and not between them

how do electrons move between orbits?

they gain energy from the photons

the color of a photon released corresponds to how

far the electron dropped

while bohr’s model is easy to understand, electrons do not

actually orbit a nucleus like planets orbit the sun

probability cloud tells us

where an electron is likely to be found 95% of the time

probability clouds predict the shape of an

electron orbital

the modern view of orbitals is not necessarily the easiest to use when talking

about bonds and useful electrons so we will stick to the shell method

a shell is a region of space around the nucleus where

electrons are likely to reside

each shell in an atom can only hold a

fixed number of electrons

the first shell holds

2 electrons and is the smallest shell

the second and third shell each hold

8 electrons and the third shell is larger than the second because it is further from the nucleus

the fourth and fifth shell hold

18 electrons each

the sixth and seventh shell hold

32 electrons each

the correct order of electrons per shell is

2, 8, 8, 18, 18, 32, 32

for example, if shell = 11 then it would be

2, 8, 1

atoms are smaller as you go from left to right in a period because of

inner shell shielding and effective nuclear charge

effective nuclear charge is abbreviated to

Z*

effective nuclear charge, or Z*, =

total number of protons minus inner shell electrons

total number of protons equals

the atomic number

inner shell electron number equals

which row element is in

going from left to right in a period, the effective nuclear charge of each element increases and

this increases the pull on each electron making the atom slightly smaller than the one before it

ionization energy is the

energy neded to remove one electron from an atom

ionization energy increases as you go from

left to right and decreases as you go down the table