What holds an atom What holds an atom together?together?

Fundamental Forces in NatureFundamental Forces in Nature

Gravity-Gravity- universal attraction of all objects universal attraction of all objects to one anotherto one another

Electromagnetism-Electromagnetism- Attraction or repulsion Attraction or repulsion based on charge or polesbased on charge or poles

Strong Nuclear Force-Strong Nuclear Force- Force holding the Force holding the nucleus of an atom togethernucleus of an atom together

Weak Nuclear Force-Weak Nuclear Force- Force causing Force causing subatomic particles to change into one subatomic particles to change into one another (causing nuclear radiation)another (causing nuclear radiation)

Quantum ForcesQuantum Forces

Gravity is described by Einstein’s general Gravity is described by Einstein’s general relativity. relativity.

General relativity and quantum mechanics General relativity and quantum mechanics contradict each other.contradict each other.

Normally general relativity is used for Normally general relativity is used for larger bodies (a baseball) and quantum larger bodies (a baseball) and quantum mechanics is used for smaller objects mechanics is used for smaller objects (electrons) (electrons)

Quantum MechanicsQuantum MechanicsQuantum mechanics describe how forces Quantum mechanics describe how forces

and motion work at an atomic level.and motion work at an atomic level.The word quantum is from the root “quanta-” The word quantum is from the root “quanta-”

meaning how much (quantity)meaning how much (quantity)Energy only comes out of an atom in Energy only comes out of an atom in discrete discrete

amountsamounts (specific numerical amounts- little (specific numerical amounts- little chunkschunks) ~it works like getting $ change) ~it works like getting $ change

Say someone owes you $3.25Say someone owes you $3.25The only money you can get from them come The only money you can get from them come

in the in the discretediscrete amounts of $1, 50 amounts of $1, 50¢, 25¢, 1¢, 25¢, 100¢, ¢, 5¢, or 1¢ 5¢, or 1¢

How atoms release energyHow atoms release energy

atoms can absorb energy causing atoms can absorb energy causing electrons to “electrons to “jumpjump” to a state of higher ” to a state of higher energy. energy.

This is called an This is called an excited stateexcited stateElectrons will leave ground configuration Electrons will leave ground configuration

(electron configurations we have been (electron configurations we have been drawing), and move to higher energy drawing), and move to higher energy positions positions

When electrons return to ground state they When electrons return to ground state they release energy in discrete amounts.release energy in discrete amounts.

How do we knowHow do we knowWhen atoms “drop” from an excited state When atoms “drop” from an excited state

back to ground they emit energy as light.back to ground they emit energy as light.LightLight refers to all of the electromagnetic refers to all of the electromagnetic

spectrum, not just the colors we can see.spectrum, not just the colors we can see. Infrared, ultraviolet, radio waves, and Infrared, ultraviolet, radio waves, and

microwaves are all types of light like Red, microwaves are all types of light like Red, Orange, Yellow, Green, Blue, (Indigo) and Orange, Yellow, Green, Blue, (Indigo) and Violet.Violet.

All travel at c (the speed of light 3 x10All travel at c (the speed of light 3 x1088 m/s) m/s)The difference between these is their The difference between these is their

frequency, wavelength, and energy.frequency, wavelength, and energy.

EM SpectrumEM Spectrum

/frequency

Neils BohrNeils BohrBohr saw, when he dispersed (put it Bohr saw, when he dispersed (put it

through a prism to separate it) light from a through a prism to separate it) light from a hydrogenhydrogen light bulb, distinct bands of light bulb, distinct bands of colors instead of a smooth transition.colors instead of a smooth transition.

What you would expect

What he actually saw

Hydrogen light bulbHydrogen light bulbA hydrogen light bulb works like a neon A hydrogen light bulb works like a neon

light.light.Electricity goes through the gas. All the Electricity goes through the gas. All the

atoms jump to an excited state. When atoms jump to an excited state. When they fall back to ground state, they give off they fall back to ground state, they give off energy as light.energy as light.

Since we only see bands of light (when Since we only see bands of light (when dispersed), we know energy is coming out dispersed), we know energy is coming out in in discretediscrete amounts, not a steady flow. amounts, not a steady flow.

Energy LevelsEnergy Levels

From this, Bohr determined electrons were From this, Bohr determined electrons were at certain energy levels from the nucleus.at certain energy levels from the nucleus.

Excited eExcited e- - ’s jump to higher energy levels, ’s jump to higher energy levels, then fall back to ground.then fall back to ground.

Since the distance it “falls” back is always Since the distance it “falls” back is always the same, energy always comes out of an the same, energy always comes out of an atom in atom in discrete amountsdiscrete amounts..

The energy level are the numbers on the The energy level are the numbers on the left column left column

What keeps electrons near?What keeps electrons near?electromagnetic forceelectromagnetic force like charges repel, opposite charges attractlike charges repel, opposite charges attractThe eThe e-- are attracted to the positive nucleus but are attracted to the positive nucleus but

repelled by every other erepelled by every other e--..This is why we have to fill all up arrows before This is why we have to fill all up arrows before

pairing electrons up (they don’t want to be next pairing electrons up (they don’t want to be next to each other). to each other).

Pauli Exclusion Principle ~ You can not have Pauli Exclusion Principle ~ You can not have more than two electrons in one orbital (on the more than two electrons in one orbital (on the same line) because of this repulsion.same line) because of this repulsion.

Orbitals instead of orbitsOrbitals instead of orbitsWith simple orbits electrons would be pulled With simple orbits electrons would be pulled

into the nucleus.into the nucleus.An orbital is just the area with the highest An orbital is just the area with the highest

probabilityprobability of finding an electron. of finding an electron. The high energy of the electrons keeps them The high energy of the electrons keeps them

spinning around randomly.spinning around randomly.We do NOT know how an electron moves!We do NOT know how an electron moves!Heisenberg’s Uncertainty Principle ~ we can Heisenberg’s Uncertainty Principle ~ we can

never know exactly where an electron is and never know exactly where an electron is and where it is going at the same time.where it is going at the same time.

OrbitalsOrbitals are represented by the lines you are represented by the lines you place the arrows onplace the arrows on

This is kind of how we assume an This is kind of how we assume an electron travelselectron travels

e-

Orbitals take on different shapesOrbitals take on different shapesThe easiest (lowest energy level) shape an The easiest (lowest energy level) shape an

orbital can take is called s (sphere).orbital can take is called s (sphere).The first energy level can hold 1 s orbital The first energy level can hold 1 s orbital

only.only.The second energy level can hold 1 s The second energy level can hold 1 s

orbital and 3 p orbitals (p orbital is a higher orbital and 3 p orbitals (p orbital is a higher energy shape than s)energy shape than s)

The third can hold 1 s orbital 3 p orbitals The third can hold 1 s orbital 3 p orbitals and 5 d orbitals.and 5 d orbitals.

http://orbitals.com/orb/http://orbitals.com/orb/

More protonsMore protonsThe more positive the nucleus the closer the The more positive the nucleus the closer the

electrons can be pulled in.electrons can be pulled in.This is why we have to skip d and f (only a This is why we have to skip d and f (only a

larger nucleus can squeeze all those orbitals larger nucleus can squeeze all those orbitals into one energy level).into one energy level).

Aufbau principle- electrons will occupy the Aufbau principle- electrons will occupy the lowest energy orbital available.lowest energy orbital available.

If electrons were forced to be in the same If electrons were forced to be in the same orbital, it is assumed they would spin in orbital, it is assumed they would spin in opposite directions (to avoid contact). This is opposite directions (to avoid contact). This is represented by either an up or a down arrow.represented by either an up or a down arrow.

What holds a nucleus together?What holds a nucleus together?Strong Nuclear Force-Strong Nuclear Force- holds the nucleus holds the nucleus

togethertogetherEM forces want to blow the nucleus apartEM forces want to blow the nucleus apartNeutrons lessen this effect Neutrons lessen this effect Without enough neutrons the atom will break Without enough neutrons the atom will break

apart.apart.This process is called radioactive decayThis process is called radioactive decayFor some isotopes this happens very quickly For some isotopes this happens very quickly

(radioactive stuff) but for most it doesn’t.(radioactive stuff) but for most it doesn’t.

Odds and endsOdds and ends

Going from atoms (microscopic) to Going from atoms (microscopic) to useable amounts (macroscopic) of useable amounts (macroscopic) of

substancessubstanceschemists do not talk about the number of chemists do not talk about the number of

atoms in a reaction because atoms are so atoms in a reaction because atoms are so small.small.

Instead they refer to moles of atoms.Instead they refer to moles of atoms.1 mole = 6.022 x101 mole = 6.022 x102323 particles particlesThis is Avogadro’s numberThis is Avogadro’s number

Law of multiple proportionsLaw of multiple proportions

The same elements may combine to form The same elements may combine to form several different compoundsseveral different compounds

For example H and O can combine form For example H and O can combine form HH22O (water) and HO (water) and H22OO2 2 (hydrogen peroxide) (hydrogen peroxide)

C H and O may form alcohol, formaldehyde, C H and O may form alcohol, formaldehyde, ether (starting fluid) or many other things.ether (starting fluid) or many other things.

basically if you see a couple of elements basically if you see a couple of elements don’t assume they can only go together one don’t assume they can only go together one way.way.

Law of conservation of massLaw of conservation of mass

~ mass is neither created nor destroyed in ~ mass is neither created nor destroyed in a reaction.a reaction.

The mass of the products must equal the The mass of the products must equal the mass of the reactants.mass of the reactants.