Atoms and the Periodic Table

Matter• Matter is everything around you that has mass.

• Anything you can see, touch, taste, or smell is matter! ◦ Air◦ Desks◦ People◦ Soil◦ Plants

What is it that makes up matter?!

Matter•What is matter made of? Is it all the same?

• Democritus (460 B.C. - 370 B.C.) was a Greek philosopher believed the universe was mostly empty space and tiny bits of stuff.• He didn’t know what the stuff was

but he knew it must be REALLY small!• So small it could not be broken into

anything smaller

The Chalk Conundrum! If you break a piece of chalk in half…is it still chalk?

When is it no longer chalk?

Can you make matter?• Democritus never explained where matter came from or where it could go

• People just guessed that matter could change into different types of matter

Can you make matter?Matter cannot be created or destroyed!

• If a space shuttle leaves Earth with astronauts and food and water and air weighing 10,000 lbs. it will return weighing 10,000 lbs.

Matter• Atom – small particle that makes up matter

•Atom in Greek means “cannot be divided”

Parts of an Atom• Atoms are made of only 3 different things

• Protons – positive charged particle•Neutrons – particle with no charge• Electrons – negatively charged particle

•Nucleus – center of the atom made up of protons and neutrons• Protons and neutrons are found in the nucleus or center of the

atom• Electrons are found outside the nucleus

Parts of an Atom Electrons are so small as it is we hypothesize that they aren’t made up of anything smaller

Protons and neutrons however… Quarks – smaller particles that compose protons and neutrons of an atom

◦ 6 unique quarks have been discovered◦ It took almost 450 scientists several years to discover the 6th quark!

How big are Atoms?• SMALL! Really, really, really, really, small…

The Atomic Model• So what exactly does an atom look like?!

• Scientists have developed models over the years to explain how atoms work…

Gold Foil Experiment• Rutherford was one of the first to propose that atoms had a dense nucleus

• Gold foil experiment• Particles were fired at a piece of

gold foil• Most went straight through• Some were deflected

Electron Cloud Model• By 1926, scientists had developed the electron cloud model of the atom

• Electrons do not follow fixed orbits

•Instead they occur frequently in certain areas around the nucleus at any given time

What is in an Atom?•

Bohr Model• The Bohr model represents an atom by using rings drawn around the nucleus with dots to represent electrons

• Orbital – each ring of electrons in an atom• The 1st orbital can only hold 2 electrons!• The following orbitals can only hold a

maximum of 8 electrons

Atoms• Element – a known substance that cannot be broken down into another substance◦ Made of only one kind of atom

Sulphur (S) Potassium (K) Aluminum (Al) Chlorine (Cl)

Periodic Table• Periodic Table – a chart that organizes elements by the number of protons they have in the nucleus

• Elements are listed by their chemical symbols• Aluminum = Al• Calcium = Ca• Gold = Au• Oxygen = O• Hydrogen = H• Carbon = C

How to Read a Periodic Table• Dimitri Mendeleev, a Russian Chemist, developed the first periodic table• Mendeleev based his table on the mass of the atoms• “I began to look about and write down the elements with their atomic weights and typical

properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.”

• A British chemist later improved upon the periodic table by rearranging the elements based on their atomic number (the number of protons).

Atomic Number• Atomic number – the number of protons found in a single atom of the element

• The periodic table is arranged based on these numbers

Atomic Mass• If you were asked how tall you were, would you answer in kilometers?

•NO! You would use an appropriate unit! (cm, or m)

•Scientists had to develop an appropriate unit for the mass of atoms since they were so tiny!

•Atomic mass unit (amu) – unit of measure used for atomic particles

•Atomic mass – the mass of an atom of the element

Atomic Mass• How do we calculate the atomic mass?

• 1 proton is equal to almost exactly 1 amu

• 1 neutron is equal to almost exactly 1 amu

• Electrons are so tiny they make little difference

How Many Neutrons?• The number of protons in an atom is equal to the element’s atomic number

• The number of electrons in a neutral atom are equal to the number of protons◦ 1 positive and 1 negative equals 0!

• Often, the number of neutrons is equal to the number of protons but NOT ALWAYS!

• Krypton Has an atomic number of 36

• Number of protons?

• Number of electrons?

• Number of neutrons?• Round the atomic mass to the nearest whole

number• 83.80 84• 84 – 36 protons = 48

36

How Many Neutrons?

36

Reading a Periodic Table• All the rows read from LEFT to RIGHT

• Each row is called a period

• The period an element is in tells you how many electron orbitals are present• Elements in the top period have 1 orbital• Elements in the 3 period have 3 orbitals

Reading a Periodic Table• The vertical columns of the periodic table are called groups

•Elements found in the same group have the same number of electrons in their outer orbital

• Valence Electrons – the electron in the outermost ring of an atom• Elements in group 1 have 1 electron in

their outer shell• Elements in group 4 have 4 electrons in

their outer shellThe middle “transition elements” don’t follow

this rule! We’ll talk about them later on…

Try it!• Nitrogen• Atomic number?

• Number of protons?

• Number of electrons?

• Number of neutrons?

• Atomic mass?

• Number of valence electrons?

14

7

7

7

7

7