2.1 Nature of Matter

Atom – atomos – “unable to cut”

- basic unit of matter which consists of 3 Subatomic particles.

Proton

• Location: in the nucleus (center)

• Mass: 1 atomic mass unit (amu)

• Charge: Positive (+1)

Neutrons• Location: in the nucleus

• Mass: 1 amu

• Charge: no charge (neutral)

Electrons• Location: outside of nucleus in orbitals

(electron clouds, energy levels)

• Mass: nearly 0 amu

• Charge: Negative (-1)

Electron Orbit (not really)• Electrons in fact inhabit regions of space

known as orbitals – undefined paths.

• You can think of an orbital as being the region of space in which the electron lives (clouds).

Element

• Def – a pure substance that consists entirely of one type of atom.

• Ex - Gold

Using the Periodic Table

• Detailed information about elements

• Strategically Arranged

Periodic Table

Group – elements in the same column, react in the same ways

Period – elements in the same row, have similar physical properties

Chemical Symbols

6

C12.011

1 – 2 letter chemical symbol

Atomic Number

Atomic Mass

Atomic Number – the number of protons found in the atom

Atomic Mass – the total number of neutrons and protons in the atom. (Units: amu)

Try These

11

Na23

How many protons? 11

How many neutrons? 12

Element Name? Sodium

30

Zn65.5

How many protons?

How many neutrons?

Element Name?

30

35 - 36

Zinc

Isotopes

Def: atoms of an element that have different number of neutrons

• All isotopes have the same chemical properties. Why?

Radioactive Isotopes• Def: isotopes that have unstable nuclei that become stable by releasing radiation

– Uses of Radioactive Isotopes• Determine the age of rocks because the nuclei break down at a constant rate.• Treat Cancer

Compounds

Def: a substance formed by the chemical combination of two or more elements in definite proportions

NaCl - Salt H2O - Water C6H12O6 - Glucose

Forming Chemical Compounds

Ionic Bonds – a bond formed when electrons are transferred from one atom to another.– Ions: atoms of the same element that have lost

or gained an electron.

– 2-8-8(18) Rule: Elements want to fill their outer shell by gaining or losing electrons.

Valence Electrons

Valence Electrons: Electrons in the outermost shell of an atom.

Ionic Bonding

Covalent BondsDef: A chemical bond that forms when

electrons are shared between atoms.

Think about Hydrogen

Animation

Molecule: the smallest unit of most compounds.

Covalent BondsWhy does Carbon usually form covalent bonds, instead of ionic bonds?

Answer – Outer shell is half full.

Van der Waals Forces• Sometimes in covalent bonds the sharing of

electrons is not always equal.

• Slight attraction between slightly charged regions of a nearby molecules.

• A combination of ionic and covalent bonds

TED - Gecko Talk

Basic observations about water1. Use your pipette to make droplets of water on

your desk. Write down any observations you made.

2. What happens if you make one drop very near to another one?

3. Use the penny I gave you as a surface to drop water on. See how many drops of water can be held on the surface of the penny before it spills.

4. Lastly, look at the inside of the pipette after you’ve squeezed all the water out. What do you notice?