CAPTER 1: ATOMIC STRUCTURE

What is Atomic Mass?

Mass number=protons+neutrons In this picture you have 2 atoms: -one atom has 5 protons and 5 neutrons and mass number of 10 (5+5=10) and Atomic Mass of 10 AMU (notice that Atomic Mass is in units vs. mass number is not-its just the total number of protons and neutrons) -the other one has 5 protons and 6 neutrons and mass number of 11 (5+6)=11 and atomic Mass of 11AMU Mass number tells us how many protons and neutrons atom has vs atomic weight tells us how much the atoms weights in AMU.

Lets now discuss what is MOLE?

Mole describes number of things (atoms, ions, molecules) 1 Mole has 6.02x10²³ things. These things can be ether atoms, ions, molecules...

When you think of ISOTOPES you must think of:

NEUTRONS

What are ANIONS?

Negatively charged atom since it gained one electron. Net charge -1

Isotopes have specific notations:

On the bottom there is Atomic Number (protons only) -A On the top you have Mass Number (protons+neutrons)- Z

Lets now discuss what all these numbers mean?

One thing is that all the atoms that have p⁶ configuration are going to be very stable. They won't react with other things.

So what makes up Nucleus of the Atom?

Protons and Neutrons and they together make up MASS NUMBER

Electrons move around nucleus and are only located in specific ENERGY LEVES called

SHELLS Electrons closer to the nucleus are in Lower energy levels vs the electrons further away from the nucleus are in higher energy levels.

PRINCIPAL QUANTUM NUMBER has symbol n and it tells us the energy level or the size of the orbital. The higher the number the larger the orbital is. Lets use Si as example:

Si electron configuration is: 1s²2s²2p⁶3s²3p2 Si has the last electrons in 3p² orbital. 3 indicates the Principal quantum number. So in here the principal number is n=3

Now lets look the the Silicon electron configuration: How many electrons will have the quantum number n=3

Si electron configuration is: 1s²2s²2p⁶3s²3p² The last electrons are located in 3p² The answer is 4 electrons. 3s² and 3p² electrons

ELEMENT (gold)→Atom (basic unit of element)→Nucleus (protons and neutrons with electrons located outside)

So think about this in the way that you are braking down element to its smalls units.

Notice the numbers going from 1-7. There are the energy levels of the electrons. The number increases as you move down.

The higher the number the more energy electron has.

Now lets now learn how to calculate molar mass using chemical formula: SO₂

This means that 1 mole of SO₂ weights 64.07grams

Why does electron just fly away from atom?

electrons have negative charge and they are attracted to positively charged protons in the nucleus.

How many electrons doe Al has?

it has 12 protons so it must have 13 electrons. The configuration of the elections is: 2 1s electrons 2 2s electrons 6 2p electrons 2 3s electrons 1 3p electron

When you are assigning the number to the orbital:

s has l=0 p has l=1 d has l=2 f has l=3

Lets recap:

-Atomic number (Z) is # of protons in nucleus -Mass number (A) is # of protons and neutrons in nucleus -Number of protons is equal to number of electrons in neutral atom -Electrons are not included in mass calculations because they are too small.

What are PROTONS:

-They are found in the nucleus of the atom (in the center) -They have charge of +1 -They have mass of 1AMU -When you look at the periodic table you will notice that elements are organized in order of the ATOMIC NUMBER which is the number of protons on the element.

Problem #1 You have 31.87g of carbon how many moles do you have?

1 mole =12.01g 31.87g/12.01g=2.654 moles

Now lets find out how many atoms we have in the 2.654moles of the carbon?

2.654moles x 6.02x10²³

Calculating the Atomic weight of Boron atom?

20% x 10AMU + 80% x 11AMU=10.8AMU So the atomic weight is closer to 11AMU then 10AMU and this makes sense since 80% of Boron weighs 11AMU.

Remember that protons and neutrons are in the center of atom:

And they create NUCLEUS!!!

Common mistake that students make. Problem #2: How many moles are in 29.4L of liquid ethanol at STP?

As you can see you are in STP so what is the problem? In here we are talking about liquid ethanol and the conversion factors only work for gases!!! Make sure you are working with gases!!!

What is Atomic Mass:

Atomic Mass is measure in units of Atomic Mass units and its defined using Carbon 12. Carbon 12 has a mass of 12AMU. Since proton has a mass of 1AMU and neutron has a mass of 1AMU and carbon has 6 protons and 6 neutrons this will add up to 12 in total making it 12AMU.

Next: Bohr Model of atom.

Both also confirmed that there is a nucleus in the middle of the atom and its positively charged but he discovered that electrons are not randomly distributed through the atom. He discovered that electrons are in ORBITS and they spin around the nucleus just like the orbits. This model was closer but it was not 100% correct since the electrons are not in Orbits and are not orbiting around nucleus. But he was closer to getting the correct model of atom.

Example of Isotopes is: Carbon

Carbon has 3 naturally occurring isotopes Carbon 12, 13 and 14 and they are present in different percentage on Earth. Notice the difference in the neutrons.

Protones define elements!!!

Carbon has 6 protons. You can't have Carbon with 7 protons that will be Nitrogen.

But not all the atoms weight the same amount. Some are more heavy vs some are less heavy.

Carbon weights 12.01g Zinc weights 65.38g So when you want a mole of atoms which are 6.02x10²³ atoms you weight out the specific amount. For Carbon you weight out 12.01g and this will give you 1 mole or 6.02x10²³ carbon atoms-you don't have to count atoms!!! You count atoms by weight out the atoms.

Lets now focus on the Planck relation equation: E=hf

E is energy of each photon in Jules f is the frequency of light measured in Hz h is Planck constant

Next: Ernest Rutherford experiment of Gold Foil

He discovered that atoms had positive nucleus and it was concentrated in the center of the atom. Beside the center where the nucleus was located atoms were empty space. So Thompson though that the positive charge was distributed through the atom but Rutherford showed that the positive charge is only located in the center of the atom.

Next: The Quantum Mechanics Model by Schrodinger.

He showed that electrons are not spinning in orbits but rather they are in different pathways with specific shapes around the atom. He called the locations of the electrons ORBITALS not ORBIT.

The table with all the numbers represents the information about the location of the electron.

Hydrogen has 1 electron and its called 1s electron. Li is 2s¹ which means that it has 3 electron.

Must Remember: While Atom always have the same number of protons they might have different numbers of neutrons. Atoms that share the Atomic Number but differ in Mass number are called?

ISOTOPS

What happens when element gains or looses electrons?

In neutral state element has the same number of protons and electrons. That way charges cancel out and atom is neutral. But when element looses electron it looses negative charge it becomes less negative and more positive since it has one extra net proton which has net +1 charge. When it gains electron it becomes more negative.

Now notice the small numbers on top.

In s block there are 1 and 2 In d block they are 1-10 In p block they are 1-6

Lets now look how we can use moles to count the number of atoms we have in something?

It would be very difficult to count individual atoms of sulfur and it would take forever!!! But what if we know that 1 mole of sulfur which is 6.02x10²³ equals to 32.07g.

Problem: What is the mass number and Atomic Mass of Carbon 12?

Mass number=12 since there are 6 protons and 6 neutrons Atomic Mass=12AMU since you have 6 protons and 6 neutrons and each weights 1AMU which makes it total of 12AMU

What is the mass of one proton?

1AMU

AMU can be converted to grams since:

1AMU=1.660x10⁻²⁴grams But again this will be very small number... not very useful.

So the last electrons added to silicon: Si electron configuration is: 1s²2s²2p⁶3s²3p2

3p² has l=1 and n=3

Example #1 You are thinking a blue light of frequency 6.2x10¹⁴ Hz on the pice of metal causing electrons to be produces from the surface. How much energy does each of the photons contain?

E=hf E=6.626x10⁻³⁴Js x 6.2x10¹⁴ Hz=

The main thing to remember is that in neutral atom the number of electrons is the same as number of protons.

Each electron needs to have specific configuration.

Next lets lear Converting Between Moles and Liters of a Gas at STP.

Must remember that at STP 1 mole of gas will take up 22.4L of volume

What is the symbol of ATOMIC NUMBER?

Z

So lets sum up:

-Atomic number= #of protons -Mass number= # of protons + #number of neutrons -Atomic Mass= expressed in Units AMU # of protons+ # of neutrons in nucleus (1 proton has a mass of 1AMU and 1 neutron has a mass of 1AMU) -Atomic weight= take the % of the isotopes into account and its found on the bottom of periodic table

lets move on to the NEUTRONS:

-Neutrons do not have a charge -Neutrons and protons are almost the same mass so they make up the mass of Atom (electrons are very small) -Every Atom has Mass Number (A) which is the number of Protons + Neutrons

Atom is made out of the subatomic particles. For MCAT you need to know 3 subatomic articles:

-Protons -Neutrons -Electrons

What are ELECTRONS?

-they are NOT located in nucleus rather they surround nucleus -they are located in SPECIFIC levels of energy (electrons move around nucleus in specific distances) -they have -1 charge -electrons are the one that are involved in creating chemical bonds and they determine reactivity. So electrons can move to different atoms or they can be shared by two atoms.

Valence Electrons:

-they are located the furthest away from the nucleus therefore they experience the least amount of the electrostatic pull from their own nucleus. -valence electrons determine the reactivity of the element -they are involved with creating chemical bonds between the atoms -its important to understand that elements want to fill their highest energy levels with electrons and this will increase elements stability.

the number 6.02x10²³ is referred to as AVOGARDOS NUMBER

1 mole is equal to Avorgado number 6.02x10²³ So one mole of sulfur means that you have 6.02x10²³ sulfur atoms.

But do you know that 1 mole of the sulfur atom weight 32.07g?

All you have to do is look at the periodic table and atomic weight that is on the bottom of the table.

Common mistake that students make. Problem #1 What is the volume in liters of 10.3 moles of oxygen O₂ gas at 25°C and 2ATP of pressure?

As you can see you can't use the simple mole conversion in here since you are NOT at STP!!! In this case you must use the ideal gas law. You will learn this later!

ATOMIC NUMBER vs. MASS NUMBER:

Atomic Number: -number of protons -Symbol Z -elements always have the same Atomic number which is the number of protons Mass Number: -number of protons and neutrons -Symbol A -elements can have different number of neutrons which results in ISOTOPES

How Many protons, electrons and neutrons the Isotope of U Has?

Atomic Number=92 which is the number of protons Mass number=235-92=143 neutrons And for the atom to be neutral it must have 92 electrons.

So ISOTOPS HAVE THE SAME:

Atomic number but they have different mass number

So one important thing to remember about protons and atomic number is:

Atomic number is the number of protons and it acts as identifier of the element since elements are defined by number of protons they contain. So carbon has 6 protons but if there are 7 protons its no longer carbon its Nitrogen.

How Many protons, electrons and neutrons This Isotope of Carbon Has?

Atomic number=6 so it must have 6 protons Mass number=12 so it must have 6 neutrons For this Carbon to be neutral it must have 6 electrons as well.

How Many protons, electrons and neutrons This Isotope of Carbon Has? This is called Carbon 13 and its one of the isotopes of Carbon.

Atomic number=6 so it must have 6 protons. Mass number=13 so it must have 6 protons and 7 neutrons This Carbon is neutral so it must have 6 negative electrons to balance 6 positive protons.

Atomic weight of Carbon 12:

Atomic weight is also measure in Atomic Mass unit but its not a mass of one atom like Carbon 12 but its average of the isotopes of specific atom. So Carbon has many isotopes and they are present on Earth in different percentage. So Carbon 12 makes up 99% of the carbon but there is 1% of the Carbon 13. So Atomic Weight takes all of the isotopes in consideration. Atomic weight=12.01 since 99% of the Carbon on Earth is Carbon 12 not Carbon 13.

You can notice that on the picture you have atoms with the same number of protons but only differ in number of neutrons. Which means they are isotopes. There are two isotopes of Boron: Boron-10 and Boron-11

But only 20% of Boron is Boron-10 and 80% is Boron-11. So Atomic weight takes in consideration the percentage of the isotope present on Earth. Atomic Weight asks: What is the AVRAGE MASS of Boron Atom?

Lets now talk about ATOMIC MASS UNIT and what it is? Since atoms are so small chemist came up with AMU

Chemist took the mass of one Carbon 12 atom as a definition of 12AMU 1Carbon 12=12AMU

The last quantum number is the SPIN QUANTUM NUMBER and it deals with the spin of the electrons and it has symbol of s or ms

Each orbital can hold up to 2 electrons and each of the electrons will have different spin. This will be representative by +½ or -½

SO what can change in atom?

Electrons and Neutrons can change. But if you change protons you will have different atom/element.

What is atom?

Elements are made out of single unit called ATOM. Atom is the smallest unit that contains characteristics and properties of element.

First lets ask ourselves what are elements?

Elements are pure substances such as gold, carbon or lead in their purest form and they are all listed on the periodic table of elements. Water is not element. Most basic unit of the element is ATOM. Carbon atom, gold atom, lead atom... and you can't brake down this anymore and call this lead or carbon. You get something different.

Where is ATOMIC NUMBER located on the periodic table?

Its on the top of the element.

What is MASS NUMBER?

Its the number of protons and neutrons in the nucleus.

What is ATOMIC NUMBER?

Its the number of protons that element have.

Lets now move on to Atomic Weight:

Its the number that is reported on the bottom of the periodic table. And the main thing to remember that atomic weight takes in consideration the percentage of the isotope that is present on Earth.

Lets move on to the next topic: Models of the Atom through History JJ Thompson

JJ Thompson discovered that atoms have electrons and that electrons are small and inside the atom. He called this model the Plum Pudding Model where it looks like blubbery muffin (so if you open the muffin the elections would be stuck inside just like bluchers in muffin and they were negatively charged and the doe of muffin was positive charge to keep the negative charges of electrons balanced).

Mark Plank developed first Quantum model and it describes the size of the energy packets-QUANTA that are contained within light. The packages of energy are called PHOTONS.

Plank constant is given h symbol and its equal to 6.626x10⁻³⁴Js So he discovered that light is not continues quantity and can have any value but rather light contains a packages of energy called PHOTONS.

What are CATIONS?

Positively charged atom since it lost electron. Net charge +1

How come isotopes have different masses?

The reason for this is because they have different number of neutrons. Example is Hydrogen and its 3 isotopes: They all are going to have the same number of protons and electrons but they will have different number of neutrons. Also, electrons have almost no mass so the only mass of the atom is due to protons and neutrons. But since Protium has no neurons vs. Tritium has 2 they will have different masses. Thats why isotopes have different MASS NUMBERS!

Lets now focus on the Electron configurations: in here we will only focus on the atoms that are neutral that means that they have the same amount of protons and electrons.

The way that atom acts in Not depending on how many electrons it has but how they are arranged. You can see the arrangement of the electrons on the periodic table.

Now lets move on to the ANGULAR MOMENTUM OF the electrons: s, p, d, f

These represents the shape of the orbital

So what is Atomic Mass and how does it differ then Atomic weight?

They are really the same things but: Atomic Mass tells you a number of neutrons and protons. Atomic Weight tells you the weight of the atom in AMU and since neutron and proton each weights 1AMU atom with 6 protons and 6 neutrons will weight 12AMU.

This chapter will focus on the atom and the structure of the atom.

Through history humans notice that we have different elements like carbon, gold that have specific properties. Some might reflect light while other might be gas in room temperature. These are the substances that are pure and naturally occurring on Earth. But we might ask if you keep braking down the carbon or gold can you brake it down to some smallest unit that still has properties of carbon? And if you brake down that small unit it does no longer have the properties of the element? Yes-and its called atom.

Electrons that are furthest away from the nucleus have the least amount of interactions with nucleus and therefore they can interact more strongly with environment and other atoms. The name of the electrons that are furthest away from the nucleus is:

VALENCE ELECTRONS

Lets now discuss 4 Quantum numbers: Principal, Angular momentum, Magnetic Spin

We have 4 ways to describe the properties of the electron by 4 quantum numbers.