2.1 Composition of Matter Weight Mass Anything which occupies space and has mass Weight The effect of gravity on something Mass The quantity of matter an object has Ex. A person would weigh less on the moon but still have the same mass (less gravity on the moon)

  Elements Pure substances which cannot be broken down chemically into simpler kinds of matter More than 100 elements exist *109 exist, 92 are naturally occurring Most important for living things are carbon(C), hydrogen(H), oxygen(O), nitrogen(N). 96% of mass of living things is made up of these four elements. If you add in calcium(Ca) and phosphorous(P), then you have 99% mass of all living things.

Periodic Table of the Elements Atomic number (number of protons) Chemical symbol Atomic mass (number of protons and neutrons) Chemical Elements.com - An Interactive Periodic Table of the Elements

Atom Simplest part of an element which has the properties of that element Energy levels Nucleus Electrons (2,8,8)

Nucleus Central core of an atom Contains protons (positive electric charge) and neutrons (neutral charge)

Electrons Electrons (negative electric charge) are found in the outer shells of the nucleus. In a stable atom, the number of protons equals the number of electrons. Thus, the atom has a net charge of 0. Electrons are high-energy particles with very little mass (1/1800 of a proton). They are found in energy levels of the atom, moving at high speed. They have more energy in the outer most shells.

How many atoms make up each of the following compounds. 1 How many atoms make up each of the following compounds? 1.   CH4 methane 2.   NH2CH2COOH glycine 3. (NH4)2SO4 ammonium sulfate

Molecules   2 or more atoms combined which form a substance and can exist in a free state EX. H2, and O2, and Cl2

Compounds Atoms of 2 or more different elements combined. This is how most elements exist in nature EX. NaCl and H2O

Elements Physical and chemical properties are different for the element alone compared to elements combined. EX. H2O vs. H2 and O2 The H2O is liquid at room temperature while H2 and O2 are gases at room temp. Most elements are not stable in nature. To be stable, the outer energy level has to be full. EX. Neon (Ne) atomic number 10 EX. Helium (He) atomic number 2 Both of these elements tend not to react with other elements and they are called inert gases Look at the energy shells.

Energy Shells Ne At. #10

Energy Shells He At. #2

Bonds To form compounds, elements form bonds (invisible forces) by undergoing chemical reactions. They want to fill their outer energy level to become stable. A bond can form anywhere there is 1 electron (e-). There are 2 major types of bonds which can be formed: covalent and ionic.

1. Covalent Bonds (strong) Sharing of electrons EX. Water (H2O) Hydrogen (H) has atomic number 1 and Oxygen (O) has atomic number 8

2. Ionic Bonds (weak) Giving up of electrons EX. Salt (NaCl) Sodium (Na) has atomic number 11 and chlorine (Cl) has atomic number 17 As the Na and Cl give and take electrons, they become positively or negatively charged particles called ions. The bond, which is formed between these elements, is called an electrostatic force.

Hydrogen (H) At. # 1 Oxygen (O) At. # 8

Sodium (Na) At. # 11 Chlorine (Cl) At. # 17