Atomic Theory Unit Flashcards

what was wrong with the nuclear model of the atom/rutherford’s model?

•  electron is vibrating, circling around the nucleus

• radiating light and radiation, therefore losing energy

• if energy is being lost, it should be slowing down and falling into the nucleus

• since it does not fall into the nucleus, there is a flaw in the model

what explained the problem of “collapsing” atoms

the bohr model of the atom

3 postulates of bohr model of atom

1. electrons in atoms may only occupy specific energy states called stationary states, each corresponds to a well defined circular orbit around the nucleus → energy is quantized: only has specific certain values

2. electrons in stationary states do not emit energy

3. electrons can change stationary states by absorbing or emitting a quantum of energy exactly equal to the energy difference between the two states

ground state

• lowest energy arrangement of electron

• closest state electron can be to proton

excited state

• NOT the lowest energy state

• not lowest electron arrangement in atom

• any other level besides ground

• infinite amount

electrostatic force

attraction or repulsion of electrons and protons

quantized and quantum

• Quantized: has a certain specific value

• Quantum: Something that has a certain specific value

when does an electron have greater potential energy?

greater potential energy when in excited state, the further it gets from nucleus

why doesnt the electron fall into the nucleus?

• the electron can come closer to ground state by releasing a quantum of energy

• the electron can go further from the nucleus by absorbing a quantum of energy

• it does not continuously move, can only absorb or release exact amount of energy and goes to next orbit without staying in between the orbits

• the closest the electron can be to nucleus is in ground state

nucelons

particles found in the nucleus, in our case protons and neutrons

standard atomic symbol

• A in top left corner: atomic mass number

• Z in bottom left corner: atomic number

• X: element

• charge: depends on protons and electrons

Z

• atomic number

• number of protons in nucleus

• defines identity of element

• found in top right corner on table

A

• atomic mass number

• total number of nucleons (protons and neutrons) in a nucleus

• not the mass

• will always be a whole number

• found underneath the name of an element on table

non standard atomic symbol

X - A, element dash mass number

how to determine number of protons, neutrons and electrons

• #p: Z, atomic number

• #n = Z - A, protons - electrons

• #e = same as protons unless there is a charge

• FIX THIS CARD

isotope

• different forms of the same element that contain equal numbers of protons but different numbers of neutrons

• differ in relative atomic mass but not in chemical properties

isotopes of hydrogen

• protium: one p+, zero neutrons, one e-

• deuterium: one p+, one neutron, one e-

• tritium: one p+, two neutrons, one e-

radioisotope

unstable isotope that undergoes nuclear decay

ions

• unequal number of protons and electrons

• have a charge

• electrons > protons: negatively charged anion

• electron < protons: positively charged cation

allotrope

different forms of the same element that have different physical and chemical properties, i.e. charcoal and diamond are allotropes of carbon

electronic configuration

Arrangement of electrons around the nucleus in an atom

valence orbit/shell

Outermost orbit of electrons 

inner orbit/shell

NOT the outermost orbit of electrons 

principal quantum number (n)

• use to determine total number of electrons depending on how many shells there are when shells are full

• number of electrons = 2n²

• i.e. in 3 shells, 2(3)² = 18, the first orbit has 2, then 8, then 8 again

purpose of mass spectrometer

• a sample is heated, vapourized and ionized

• travels down to the detector

• calculated force of the magnets that bend the sample

• based on the magnetic force you know the masses and you know the relative amount of the

isotope

Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element

how to determine average atomic mass?

• Calculate average of the mass of the isotopes

• Multiply masses by percentage

• add them up

Determine the average atomic mass of a sample of magnesium based on the percent composition data in the picture

MAvg = (CMg-24 x MMg-24) + (CMg-25 x MMg-25) + (CMg-26 x MMg-26)

= (0.7890)(23.98504 amu) + (0.1000)(24.985839 amu) + (0.1110)(25.982595 amu)

= 24.306852 amu

= 24.31 amu

positioning of electrons

• at 3

• at 6

• at 9

• at 12

• always fill first 4 positions before starting pairs

• for Helium, draw the two as a pair (together) at the top or right

• in the first orbit, the two electrons will always be a pair at the top or right

how to draw bohr rutherford diagram looking at periodic table

• period # = # of shells

• group # = # of valence electrons (groups 1-8)

• first orbit : max 2 pairs

• all other orbits: max 18 electrons, 4 pairs

• nucleus: # P and # N written

how to draw bohr diagram looking at periodic table

• period # = # of shells

• group # = # of valence electrons (groups 1-8)

• first orbit : max 2 pairs

• all other orbits: max 18 electrons, 4 pairs

• nucelus: no cricle around it, just element symbol

how to draw lewis diagrams

• only includes valence electrons

• He is the only one where e is in a pair on the right, all other elements have them separated (fill first 4 positions before starting pairs)

• elements name in middle

summary of gold foil experiment

• ernest rutherford

• fired alpha particles (tiny and charged particles smaller than atom) at gold foil

• found that 1 - majority of alpha α particles shoot straight through

• 2- a small fraction of alpha α particles found at small angles

• 3- tiny fraction of alpha α particles detected in front of the foil

conclusions of gold foil experiment

• most of atom is empty space

• positively charged centers consist of majority of mass

• mass and charged are not uniformly distributed

• nuclear model of atom: positively charged nucleus with electrons orbiting nucleus

electrostatic force

Force of attraction and repulsion between protons and electrons

principal quantum number

• orbits outside of nucleus

• n = 1, 2, 3… infinity

• electron is never between any two states

when electron goes closer/farther from nucleus

• gives off a quantum of energy exactly equal to the difference between the two states when going from excited to ground

• when going away from nucleus, ground to excited or further, absorb a quantum of energy exactly equal to the difference between the two states when going from excited to ground

what determines the attraction of electrons and protons

the attraction between electrons and protons depends on the number of protons

frequency is proportional to…

• frequency is inversely proportional to wavelength

• high frequency, short wavelength

• low frequency, long wavelength

incandescent light is a

continuous spectrum

are orbits of electron dynamic or static?

• dynamic

• change according to forces/function of forces

• different forces, different energy

line spectra and identifying elements

• all elements give off a different spectra

• spectras can be used to identify elements

• the spectra depends on the energy in the element which depends on the force of attraction in the atom

• electron is attracted to nucleus

• the nucleus charge/number of protons determines the force of attraction

• Every element has a different number of protons therefore different levels of attraction therefore different energy levels therefore different line spectrums

What is a key tenet of Dalton's Atomic Theory regarding elements?

Each type of atom makes up a specific substance we call an element.

According to Dalton's Atomic Theory, what happens to atoms in chemical reactions?

Atoms are never created or destroyed in chemical reactions.

How do atoms combine to form compounds, according to Dalton's Atomic Theory?

Atoms combine in simple whole number ratios to form compounds which are constant and define a particular substance.

What does measuring mass tell us about particles according to Dalton's ideas?

Measuring mass indicates the amount or number of particles, because particles (atoms) have mass.

What did William Crookes invent in the 1870s that contributed to understanding atoms?

He invented the Crookes tube.

What observation made within the Crookes tube suggested that cathode rays had a charge?

Magnets could change the polarity and move the rays.

What was J.J. Thomson's conclusion about the green glow in his Maltese cross experiment?

The green glow flows from the cathode to the anode and are negatively charged cathode rays.

What did the paddle wheel experiment demonstrate about cathode rays?

Cathode rays have mass and are made of particles because they can push the paddle wheel away from the cathode.

What did J.J. Thomson discover through quantitative experiments with cathode rays?

Cathode rays are much lighter than hydrogen atoms, and discovered electrons as the first subatomic particles.

Why did scientists believe there had to be positive charges within an atom?

Since electrons are negatively charged and matter is usually neutral, there has to be positively charged subatomic particles to balance the negative charge.

Describe the Plum Pudding Model of the atom.

JJ Thomposon: A ‘dough’ of positive charge with negatively charged electrons dispersed throughout it, with uniform mass and charge density, no concentrated areas

summary of crookes tube experiment

evacuated tube with a cathode (-) and anode (+) connected to a power supply emitted a green glow that could be deflected by magnets → it must consist of charge

summary of maltese cross experiment

a different shape of evacuated tube had a cathode at the tope and anode at the bottom, and a maltese cross at one end, when connected to a power supply emitted a green glow that created a shadow, and if polarity were switched no glow would appear → the glow travels from the cathode to anode, so they are negatively charged cathode rays

summary of paddle wheel experiment

(thompson or crookes) a paddle wheel inserted in an evacuated tube and the cathode rays caused the wheel to move → cathode rays have mass