Chemistry of Life Chapter 2

Why Learn Chemistry in Biology? Matter: anything that has mass and takes up space Matter: anything that has mass and takes up space EVERYTHING is matter; water, air, living things, etc EVERYTHING is matter; water, air, living things, etc Matter is NOT light, sound, or energy Matter is NOT light, sound, or energy ALL matter is made of atoms (living things too!) ALL matter is made of atoms (living things too!) An atom is the smallest unit of matter that cannot be broken down by chemical means. An atom is the smallest unit of matter that cannot be broken down by chemical means. An element is a substance made of only one kind of atom, and it is therefore a pure substance. An element is a substance made of only one kind of atom, and it is therefore a pure substance. All elements are found on the Periodic Table All elements are found on the Periodic Table EVERYTHING IN THE WORLD can be broken down into the elements on the table EVERYTHING IN THE WORLD can be broken down into the elements on the table

Parts of an Atom All atoms have 3 parts All atoms have 3 parts Proton: P+, positive (+) charge, found in the nucleus Proton: P+, positive (+) charge, found in the nucleus Neutron: N, neutral (0) charge (no charge), found in the nucleus Neutron: N, neutral (0) charge (no charge), found in the nucleus Electron: e-, negative (-) charge, found in the electron cloud around the nucleus Electron: e-, negative (-) charge, found in the electron cloud around the nucleus Atoms are NEUTRAL. Protons (+) are attracted to the electrons (-). Atoms are NEUTRAL. Protons (+) are attracted to the electrons (-). Atoms have the same number of protons and electrons Atoms have the same number of protons and electrons

Atoms and Elements Elements are made of only 1 kind of atom Elements are made of only 1 kind of atom Example: oxygen is an element made of only oxygen atoms Example: oxygen is an element made of only oxygen atoms Each element has a specific number of protons, neutrons, and electrons Each element has a specific number of protons, neutrons, and electrons Example: oxygen has 8 p+, 8 n, and 8 e- Example: oxygen has 8 p+, 8 n, and 8 e-

Changes in p+, n, and e- *IF YOU CHANGE THE NUMBER OF PROTONS IN AN ELEMENT, YOU GET A NEW ELEMENT!!!!! *IF YOU CHANGE THE NUMBER OF PROTONS IN AN ELEMENT, YOU GET A NEW ELEMENT!!!!! Isotope: atoms that contain different numbers of neutrons Isotope: atoms that contain different numbers of neutrons Carbon has 6 protons, 6 neutrons, and 6 electrons Carbon has 6 protons, 6 neutrons, and 6 electrons Carbon can have isotopes with different numbers of neutrons, C- 12, C-13, C-14 Carbon can have isotopes with different numbers of neutrons, C- 12, C-13, C-14 *all still have 6 protons!!!! *all still have 6 protons!!!! Ion: atoms that have different numbers of electrons Ion: atoms that have different numbers of electrons Have an overall electrical charge Have an overall electrical charge Negative if it has extra electrons Negative if it has extra electrons Positive if it is missing electrons Positive if it is missing electrons *still has the same number of protons! *still has the same number of protons!

ATOMIC STRUCTURE the number of protons in an atom and the number of electrons For Helium: p=2, e=2 the number of protons and neutrons in an atom p + n = mass number Or mass – p = neutrons He 2 4 Mass Number Atomic number number of protons = number of electrons

Counting p+, n, and e- To find the number of protons: To find the number of protons: Look at the atomic number Look at the atomic number To find the number of electrons: To find the number of electrons: Same as proton number Same as proton number To find the number of neutrons: To find the number of neutrons: Subtract protons from mass Subtract protons from mass Mass – p = neutrons Mass – p = neutrons

Bonding Atoms can combine (bond) together to form compounds and molecules Atoms can combine (bond) together to form compounds and molecules Compound: a substance made of joined atoms, can be the same element or different ones Compound: a substance made of joined atoms, can be the same element or different ones Example: H2O (water), NaCl (salt) Example: H2O (water), NaCl (salt) Molecule – a group of atoms held together by covalent bonds Molecule – a group of atoms held together by covalent bonds

Covalent Bond Covalent Bond: atoms bond together and SHARE electrons Covalent Bond: atoms bond together and SHARE electrons Molecule has no charge Molecule has no charge Water (H2O) is formed when oxygen makes a covalent bond and shares electrons with 2 hydrogen atoms Water (H2O) is formed when oxygen makes a covalent bond and shares electrons with 2 hydrogen atoms

Ionic Bond Ionic Bond: forms when 2 or more atoms gain or lose electrons and combine electrically Ionic Bond: forms when 2 or more atoms gain or lose electrons and combine electrically Ex: sodium (Na) is positive, chlorine (Cl) is negative. They form an ionic bond because the Na+ is attracted to the Cl- Ex: sodium (Na) is positive, chlorine (Cl) is negative. They form an ionic bond because the Na+ is attracted to the Cl-

Hydrogen Bond Hydrogen Bond: a weak bond formed between the hydrogen atoms in a compound Hydrogen Bond: a weak bond formed between the hydrogen atoms in a compound Water and DNA have hydrogen bonds Water and DNA have hydrogen bonds

Chemical Reactions (rxns) Molecules become rearranged into other molecules Molecules become rearranged into other molecules Bonds are broken and new ones form Bonds are broken and new ones form May release or absorb energy May release or absorb energy Reactants = starting materials (on left of rxn) Reactants = starting materials (on left of rxn) Products = ending materials (on right of rxn) Products = ending materials (on right of rxn) Same # of each type of atom must be present on each side Same # of each type of atom must be present on each side Example: NaOH + HCl  NaCl + H2O Example: NaOH + HCl  NaCl + H2O

_______________________________________

Bohr Models Bohr Model – a drawing of an atom with the correct number of protons, neutrons, and electrons Bohr Model – a drawing of an atom with the correct number of protons, neutrons, and electrons 1. Find the atomic number. Write that in the middle with a “p” next to it. Circle it. This is your number of protons 2. Find the mass number. Subtract the number of protons from the mass number. This is your number of neutrons. Write that next to the proton number with an “n” next to it. Circle it. 3. Protons and neutrons are found in the nucleus. You’ve just made that!

Bohr Models (continued) 4. Electrons are found in “shells” in a cloud around the nucleus (called the “electron cloud” Find the atomic number. This is your number of electrons 5. Shells have specific numbers of electrons that can fit 1 st shell = 2 2 nd shell = 8 3 rd shell = 8 4 th or more shells = 18

Bohr Model With Bohr Model diagrams, elements and compounds are represented by dots to show electrons, and circles to show the shells. For example; Nitrogen 7p+ 7n ⁰ XX X X XX X N

Why is water so important? 70% of your body is made of water 70% of your body is made of water Almost 70% of the earth is covered with water Almost 70% of the earth is covered with water Cells are filled with water, surrounded by water, and need you to drink water to stay healthy Cells are filled with water, surrounded by water, and need you to drink water to stay healthy Water is made of 2 hydrogen atoms covalently bonded to 1 oxygen atom (H2O) Water is made of 2 hydrogen atoms covalently bonded to 1 oxygen atom (H2O)

Properties of water Water stores heat Water stores heat A pot of boiling water takes a long time to cool down to room temperature A pot of boiling water takes a long time to cool down to room temperature A warm ocean or lake will take a long time (many months to freeze) A warm ocean or lake will take a long time (many months to freeze) Water is released from your body as sweat to help you cool down when you are hot (*homeostasis*) Water is released from your body as sweat to help you cool down when you are hot (*homeostasis*)

Properties of water Water bonds to itself and other substances Water bonds to itself and other substances Cohesion: water can bond to itself Cohesion: water can bond to itself Reason you can “overfill” a glass of water and it not spill Reason you can “overfill” a glass of water and it not spill Adhesion: water can bond to other things Adhesion: water can bond to other things Reason that dew and condensation on glasses can leave drips still attached to the surface and not fall off Reason that dew and condensation on glasses can leave drips still attached to the surface and not fall off

COHESIONADHESION

WATER MOLECULE (POLAR MOLECULE) Polarity: substances that are neutral can have ends, or “poles” that are slightly positive and slightly negative Polarity: substances that are neutral can have ends, or “poles” that are slightly positive and slightly negative Water is Polar – the oxygen is slightly negative and the hydrogens are slightly positive Water is Polar – the oxygen is slightly negative and the hydrogens are slightly positive *reason for “hydrogen bonding”* *reason for “hydrogen bonding”*

Properties of WATER Water is the SOLVENT of Life! Solute – substance that is dissolved Solvent – substance that does the dissolving Solution – a mixture in which 1 or more substances are evenly distributed in another substance

Acids Definition: a compound that donates H+ ions to a solution Definition: a compound that donates H+ ions to a solution EXAMPLE: HCl EXAMPLE: HCl In a solution, HCl breaks apart into H+ and Cl- ions In a solution, HCl breaks apart into H+ and Cl- ions

Bases Definition: a compound that removes H+ ions from a solution Definition: a compound that removes H+ ions from a solution EXAMPLE: NaOH EXAMPLE: NaOH In a solution, NaOH breaks apart into Na+ and OH- ions In a solution, NaOH breaks apart into Na+ and OH- ions

The pH Scale Definition: describes how acidic or basic a solution is Definition: describes how acidic or basic a solution is Ranges from zero (most acidic) to 14 (most basic) Ranges from zero (most acidic) to 14 (most basic) The numbers 0-14 represent a 10-fold change The numbers 0-14 represent a 10-fold change Example: lemon juice pH = 2 Example: lemon juice pH = 2 Grapefruit juice pH = 3 Grapefruit juice pH = 3 Lemon juice has 10 times more H+ ions than grapefruit juice Lemon juice has 10 times more H+ ions than grapefruit juice

pH Acid pH = 0-6 Acid pH = 0-6 Acids have more H+ ions Acids have more H+ ions Strong acid (SA) = 0-3 Strong acid (SA) = 0-3 Weak acid (WA) = 4-6 Weak acid (WA) = 4-6 Neutral = 7 Neutral = 7 Neutral solutions have equal H+ and OH- Neutral solutions have equal H+ and OH- Base pH = 8-14 Base pH = 8-14 Bases have more OH- ions Bases have more OH- ions Strong base (SB) = Strong base (SB) = Weak base (WB) = 8-10 Weak base (WB) = 8-10

Buffers Definition: substances that cause a solution to resist a change in pH Definition: substances that cause a solution to resist a change in pH Works by accepting H+ ions when their levels rise (by adding acid) or donating H+ ions when the levels drop (by adding base) Works by accepting H+ ions when their levels rise (by adding acid) or donating H+ ions when the levels drop (by adding base) Buffers work to maintain a neutral pH (7) Buffers work to maintain a neutral pH (7) Your blood is a buffer – you can eat lots of foods with acids or bases and still keep neutral! Your blood is a buffer – you can eat lots of foods with acids or bases and still keep neutral!