Nature of molecules and Properties of Water Democritus – 450 B.C. – “Cannot Be Cut”

Nature of Atoms Matter- occupies space and has mass ATOMS Central Nucleus: Protons- positive charge and Neutrons- neutral charge Electrons- negative charge - surround the nucleus –electron cloud *electrons held in place by positively charged protons

How Do You Know the Number of Protons? Atomic Number – Carbon is 6, Oxygen is 8. Typically, an atom has equal number of electrons- neutral- charges balance out Chemical Behavior is determined by electrons

How Heavy is an Atom? Atomic Mass: Sum of the masses of the protons and neutrons Measured in daltons – take 602 million million billion (6.02 X 10 23) to make 1 gram (g). Electrons weigh 1/1840 of a dalton

Isotopes Vary in number of neutrons. The atomic mass is the protons + the average number of nuetrons found in nature Carbon ----Carbon 12 – has 6 protons and ? Neutrons Carbon 13- has 6 protons and ? Neutrons Carbon 14- has 6 protons and ? Neutrons The atomic mass of carbon is Radioactive isotopes (unstable)- used in dating fossils, rocks, etc- also used in medicine (tracers) -

ELECTRONS Determine the chemical behavior of atoms Found in orbitals around the nucleus Atoms contain energy levels – The outer electrons (valence) are available to react with other atoms to form compounds or molecules

ELEMENTS IN LIVING SYSTEMS 90 elements of the 118 occur naturally Of the 90 naturally occurring elements on Earth, only 12 are found in living systems in more than trace amounts – (C, H, O, N, P, S, Na, K, Ca, Mg, Fe, Cl). Carbon, Hydrogen, Oxygen, and Nitrogen (96.3% weight of the human body) Dmitri Mendeleev – 19th century – Russian chemist- came up with one of the great generalizations – elements repeats itself in groups of eight. Repeats in the outermost shell- valence electrons (octet rule)

TRACE ELEMENTS Iodine Zinc Manganese Copper

ELECTRON ENERGY LEVELS First energy level/shell- 2 electrons Second energy level/shell- 8 electrons Third energy level/shell-8 electrons Stable elements have 8 electrons in their outer shell.

Bohr Model – Practice Hydrogen (H) Carbon (C) Calcium (Ca) Sodium (Na) Neon (Ne) Argon (Ar Chlorine (Cl)

Carbon Calcium Hydrogen Sodium Neon

Stability of Atoms Mendeleev – octet rule- need 8 electrons for a stable atom. How many to make hydrogen stable? carbon stable? How many to make calcium stable? sodium stable How many to make Neon stable? Argon stable? How many to make chlorine stable? Look at the Bohr models- Which atoms are likely to gain electrons? Which are likely to give electrons away? Think about energy (work required)

Elements, Compounds and Molecules Elements- composed of only one type of atom. The element of carbons contains only atoms. Molecule - smallest fundamental unit of a chemical compound that can take part in a chemical reaction. Compound – mixture of two or more atoms (elements) Chemical bonds- atoms of molecules join together Covalent bonds; Sharing of electrons (two non-metals) Ionic bonds: bonding between ions- transfer or receive electrons (metal and a nonmetal

Practice Bonding Gumdrops Molecule Type of Bond Gumdrop Model Dot Structure H2 Covalent

Bonding Sodium Chloride

Molecule Type of bond Gumdrop Model Dot Model NaCl ionic – metal/non

WATER – H2O

MOLECULE TYPE OF BOND GUMDROP MODEL DOT STRUCTURE H2O COVALENT

Na20 (2 sodium and one oxygen) CaCl2 (1 calcium and 2 chlorine) Do More Na20 (2 sodium and one oxygen) CaCl2 (1 calcium and 2 chlorine) CH4 (1 carbon and 4 hydrogen) CO2 (1 carbon and 2 oxygen)

WATER AND POLARITY Covalent bond- See video – https://www.youtube.com/watch?v=HVT3Y3_gHGg (water)- Crash Course Amoeba Sister- https://www.youtube.com/watch?v=3jwAGWky98c

WATER, WATER EVERYWHERE Because water is a polar covalent bond it has amazing characteristics 1. Cohesion –attraction of two like molecules – leaves pull water up from the roots, seeds swell and germinate, surface tension – gives high heat capacity 2. specific heat- do not change temperature easily- Water stabilizes temperature of organisms and the environment 3. Lower density of ice – water molecules are spaced apart when frozen- lakes freeze top down. Protects life in water 4. Adhesion- attraction of two unlike molecules – transpiration 5. Solubility- dissolves other charged or polar molecules. Blood and body fluids, cells can carry many molecules – Na, Cl, etc.