Subatomic Particles

Electron

• -ve charged particle• Outside of nucleus• Thomson’s discovery• Mass = 9.11 x 10-28g• Charge = -1.76 x 108C (coulombs)

Proton

• +ve charged particle• Inside nucleus• Rutherford’s discovery• Mass = 1.67 x 10-24g (1836x heavier than

electron)• Charge = +1.76 x 108C (opposite electron)

Neutron

• No charge• Inside nucleus• Chadwick’s Discovery• Mass of neutron = 1.67 x 10-24g (same as

proton)• Charge = no charge

Atomic Number

• This is the number of protons in an atom• Hydrogen has 1 proton and thus is atomic number 1• Oxygen has 8 protons and thus atomic number 8• Every element is different due to its different

numbers of protons• So changing the number of protons changes the

element!– Some elements may have the same electrons (ions) or

the same neutrons (isotopes)

Atomic Number

• The atomic number is found on the bottom left corner

• Atomic mass on the top left corner• Symbol in the middle

Atomic Number

• Electrons counterbalance the charge of protons– So the number of electrons in a neutral atom is the

same as the number of protons• When an electron is removed from a neutral atom– It becomes +ve because #protons > #electrons

• When electron is added to a neutral atom– It becomes –ve as #protons < #electrons

• Atoms with net charges are called ions– Net charge = #proton - #electron

Atomic Number

• We show an ion exist by putting a +/- number on the top right corner of our element

• NOTE! – Proton numbers do not change in ions

Atomic Number

• You try! Find the number of protons and electrons of the following– Uranium– Thallium– Tin– Lead– Mercury– Helium– Yttrium

Atomic Mass

• The mass of the atom• Atomic mass = #neutron + #protons• #neutron = atomic mass – atomic number• Oxygen has an atomic mass of 16. It has an atomic

number of 8. To find the #neutron, we subtract the two.– 16-8 = 8 neutrons

• Gold’s atomic mass is 197 and atomic number is 79– #neutron = 197 – 79 = 118 neutrons

Atomic Mass

• The electron is so light, it is only 1/1836 the mass of a proton and neutron that it does not contribute to the mass of the atom

• We base all our atomic masses on the mass of carbon-12. The 12 stands for its atomic mass of 12.0000g/mol or amu (atomic mass unit)

• 1 amu = 1.67 x 10-24g or the same mass as a neutron and proton

Atomic Mass

• You try, find the number of neutrons of the following. As well, what is the number of protons and electrons?– Plutonium– Einsteinium– Thorium– Gallium– Germanium– Californium

Practice time!

Isotopes

• As with ions, which is when we have different numbers of electrons

• An isotope is where the number of neutron is different

• Isotopes still have the same number of protons as the original atom

• As they have different atomic masses due to the different number of neutrons, we write their names different.

Isotopes

• We write the names with a hyphen and their mass

• Carbon-12 = regular 12 amu carbon• Carbon-13 = carbon with 1 extra neutron• Carbon-14 = carbon with 2 extra neutrons

Isotopes

• When writing them in chemical symbol format, we drop the atomic number and just write the mass

• 16O and 18O• 35Cl and 37Cl

Isotopes

• Lets take a look at hydrogen and its isotopes• Hydrogen-1 (protium)

– 99.985% of all hydrogen atoms– Most common element in our universe– Has 1 proton and o neutrons

• Hydrogen-2 (deuterium)– Has 1 proton and 1 neutron– 0.0167% of all hydrogen atoms– Used in nuclear reactors as heavy water D2O

• Hydrogen-3 (tritium)– Has 1 proton and 2 neutrons– Used in hydrogen bombs

Isotopes

• We can find the number of protons, neutrons, and electrons of an isotope as we would with a standard atom.– Just have to note the mass and that mass change

is due to neutrons

Isotopes

• You try finding the number of protons, neutrons, and electrons with the following– Uranium-238– Oxygen-18– Xenon-126– Hafnium-180

Average Atomic Mass

• Why are all the masses of elements not whole numbers?

• Why isn’t carbon 12.0000 and oxygen 16.00000 and chlorine just 35.00000 or 36.00000?

• This is due to the masses in the periodic table being averages of all the masses of the isotopes based on abundance

Example

• Carbon-12 is 98.9% abundant in nature• Carbon-13 is 1.1% abundant in nature

Average Atomic Mass Steps to solve

• Multiply each percentage as a decimal with the atomic mass

• Add up all your decimals• This is your average atomic mass that shows

up on the periodic table

Example

• Carbon-12 is 98.9% abundant in nature• Carbon-13 is 1.1% abundant in nature

Example

• Nitrogen has an average atomic mass of 14.007. The two isotopes that make up nitrogen are nitrogen-14 and nitrogen-15. What are the percent abundance of each isotope?

Average Atomic Mass

• You try– Chlorine is 75.8% chlorine-35 and 24.2% chlorine-

37. What is the average atomic mass of chlorine?

Electron Arrangements

• We look at electron arrangements in the form of Bohr models

Electron Arrangements

• Each of the noble gases outer shells are full– They satisfy the octet rule

• Outer shell electrons are also called “valence electrons”– Hence why the outer shell is usually called the

valence shell• A full outer shell is stable, it doesn’t want to

give or receive any more electrons

Remember!

• 1st Shell = 2 electrons• 2nd Shell = 8 electrons• 3rd Shell = 8 electrons• 4th Shell = 18 electrons• -----------------------------------------------------------• 5th Shell = 18 electrons• 6th shell = 32 electrons• 7th shell = 32 electrons

Remember!

• You can remember this by counting across the periodic table.

• The first row has 2 elements so 2 electrons• The second row has 8 elements so 8 electrons

and so forth!

How do other elements gain stability?

• Other elements do not have full outer shells as the noble gases do

• They will try to lose or gain electrons to get to a full outer shell

How can we tell which will lose or gain electrons?

How can we tell which will lose or gain electrons?

Carbon stability?

Summary of element stability

Why does an element want to gain or lose electrons anyways?

• Every element has an affinity for electrons– Affinity = attraction

• Some elements have more affinity than others• We measure affinity and call it electronegativity• The higher the electronegativity, the more the

element wants electrons– Fluorine has the highest electronegativity– Highest top right and weak bottom left

So how does it work?

• When two elements with differences in electronegativity come together, the one that is more electronegative draws the electron away from the less electronegative element

vs

Homework

• Page 146 #13-17• Page 147 #19• Page 149 #22• Page 150 #23 and 25• Worksheet on isotopes• Worksheet on atomic number