Atoms and the Periodic Table

• What is everything made of?

• Matter – Everything is made of matter, from the rocks to

the trees to the very air we breath!

• Particles – A small portion of matter that is infinitesimally

small (very very very small!)

• Pure substance

– it only contains one type of particle.

Atoms and Molecules

• Atoms

– the smallest particle of matter. It cannot be divided by chemical means.

– The nucleus (the center) is made up of protons (positive charge) and neutrons (no charge)

– It is surrounded by electrons (negative charge)

• Atoms are like the building blocks of the Universe!

Atoms and Molecules

• Molecule

– a group of two or more atoms held together by chemical bonds.

Atoms

Chemical

Bonds

Molecule

What is an Element?

• Element

– a pure substance that contains only one type of atom.

– Examples: Au (Gold), Pt (Platinum), N2(Nitrogen gas), O2 (Oxygen), Fe(Iron)

– It is impossible to separate an element into other substances using chemical separation techniques.

• Compound – a pure substance that contains at least two types of atoms

that have chemically combined.

– Example: H2O (water), CO2 (carbon dioxide)

– It can be separated into its constituent elements using chemical separation techniques.

Element vs Compound

• Nitrogen gas (N2) and buckminsterfullerene/”buckyballs” (C60) are not compounds, they are elements – They only contains one kind of element (nitrogen gas

contains only nitrogen and buckminsterfullerene contains only carbon)

• Things like water (H2O), table salt (NaCl), carbon dioxide (CO2), and glucose (C6H12O6) are a few examples of compounds. – They are compounds because they each contain more

than one kind of element. (ie. Water has oxygen and hydrogen atoms)

• Example of a compound

– C2H4O2 (Vinegar)

– It is made up of 3 different elements

• C = Carbon

• H = Hydrogen

• O = Oxygen

– It has 8 atoms total

• 2 carbons + 4 hydrogens + 2 oxygens = 8 atoms

• Periodic Table

– a list that groups together elements with similar properties

History of Periodic Table

• Dmitri Mendeleev

– Discovered the Periodic Table to explain relationships between the 64 elements to his students

– Predicted the existence of several elements that were later found

• The elements naturally fall into place – Each element is represented with a symbol

• It is either one or two letters

• The first letter is always a capital, the second (if there is one) is always a lowercase

• Examples: W, Hg, C, O, Be

– Atomic number • It is the number of the element

• It is based on the number of protons in the nucleus

• Ex of an element on the periodic table

– Element name

– Atomic number

– Chemical symbol

– Atomic weight

• So this element has 82 protons in its nucleus!

Group 1 Alkali Metals Group 2 Alkaline Earth Metals Group 7 Halogens Group 8 Noble Gases

The groups share similar properties. All Alkali metals are highly reactive with water. All noble gases are almost completely nonreactive. This has to do with the number of electrons in their outer most layer.

• The periodic table is divided into three parts

• Metals, metalloids, nonmetals

– Metals make up most of the table, with nonmetals making up most of the rest

– Metalloids are found between the two types, usually with a black line to separate them

• The periodic table has many more secrets to uncover!

– You can learn many things about an element depending on where it is in the table, even if you have never seen it before

• Stay in science to learn more . . .