4 KEY CONCEPT All living things are based on atoms and their interactions.

Living things consist of atoms of different elements. 4 Living things consist of atoms of different elements. An atom is the smallest basic unit of matter. Matter is anything that occupies space and has mass An element is one type of atom. Hydrogen atom (H) H O Oxygen atom (O)

An atom has 2 parts: a nucleus & electrons. 4 An atom has 2 parts: a nucleus & electrons. The nucleus is made up of protons and neutrons. Electrons float around in “energy levels” outside nucleus. Oxygen atom (O) Nucleus: 8 protons (+) 8 neutrons outermost energy level: 6 electrons (-) inner energy level: 2 electrons (-)

4 A compound is a molecule containing atoms of different elements that are chemically combined (bonded) in a fixed ratio. water (H2O) O H _ +

4 A compound is made of atoms of different elements bonded together. water (H2O) carbon dioxide (CO2) There are many other carbon-based compounds in living things!!

Warm - Up Sketch an atom. Label the nucleus, energy levels, electrons, protons, and neutrons.

4 The atoms in compounds can bond together in 2 different ways: Ionic bonds form when atoms gain or lose electrons to each other (Ionic bonds are strong bonds) Covalent bonds form when atoms share electrons (Covalent bonds are weak bonds) Analogy – baseball teams Ionic Bonds – 1 player (electron) switches to other team Covalent – The catcher catches for both teams

Ionic bonds form because of “ions” 4 Ionic bonds form because of “ions” An ion is an atom that has gained or lost one or more electrons. positive ions (made when an electron is lost) negative ions (made when an electron is gained) Therefore…Ionic bonds can form form between the oppositely charged ions! Sodium atom (Na) Chlorine atom (CI) Sodium ion (Na+) Chloride ion (CI-) Na loses an electron to CI ionic bond gained electron

Atoms share pairs of electrons in covalent bonds. 4 Atoms share pairs of electrons in covalent bonds. A covalent bond forms when atoms share a pair of electrons. covalent bonds Oxygen atom (O) Carbon atom (C) Carbon dioxide (CO2 )

4 Molecules Molecules are formed when 2 or more atoms are held together by covalent bonds. Chemical formula: tells you the number and types of atoms in a molecule (example: H2O tells you that water has 2 hydrogen atoms and 1 oxygen atom) Structural formula: shows how atoms in a molecule are connected (by bonds)

PRACTICE!!! Determine if each is the chemical or structural formula of the molecule. KMnO4 MgSO4

Chemical Reactions Chemical reaction: The breaking apart of old bonds and forming of new chemical bonds…resulting in a TOTALLY NEW SUBSTANCE. ( its like a math problem!) Reactants: starting materials for a reaction Products: ending materials from a reaction 1 + 1 = 2

KEY CONCEPT Water’s unique properties allow life to exist on Earth. Objectives: Describe the structure of a water molecule List and describe water’s unique properties Distinguish between an acid & base Explain how Earth’s conditions are fit for life

Life depends on hydrogen bonds in water. Water is a polar covalent molecule. Polar molecules have slightly charged regions. Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms. O H _ + Nonpolar molecules do not have charged regions.

Hydrogen bonds are responsible for 3 important properties of water: high specific heat - water must absorb A LOT of heat before it gets “hot” (increases temp.) 2. Cohesion: tendency of like molecules to stick together 3. Adhesion: type of attraction that occurs between unlike molecules

Cohesion & Adhesion --- DEMO Adhesion: attraction that occurs between unlike molecules Cohesion: tendency of like molecules to stick together

Explain this picture using 2 of the 3 unique properties of water!

Many compounds dissolve in water ------ DEMO. A solution is formed when one substance dissolves in another. Solvents dissolves other substances. (H2O) Solutes dissolve in a solvent. (NaCl) Aqueous Solution – any solution where water is the solvent. solution

“Like dissolves like” Polar solvents dissolve polar solutes. Nonpolar solvents dissolve nonpolar solutes. Polar substances and nonpolar substances generally remain separate.

Some compounds form acids or bases. An acid releases a hydrogen ion when it dissolves in water. high H+ concentration pH less than 7 more acidic stomach acid pH between 1 and 3

A base removes hydrogen ions from a solution. low H+ concentration pH greater than 7 bile pH between 8 and 9 more basic

A neutral solution has a pH of 7. See page 85 to view examples of Acids & Bases pure water pH 7