Chapter 2: The Chemistry of Life

Basic Chemistry ATOM: The basic building block of all matter; the smallest particle of an element that still retains properties of that element All atoms have a Nucleus, which is the central part of the atom; it contains protons; and has an overall positive charge. PROTON: (+)ve charged subatomic particles located in the nucleus; charge of +1 NEUTRON: (-/+) neutral (no charge) subatomic particles located in the nucleus; charge of 0. Protons and neutrons have about the same mass. ELECTRON: (-) Negatively charged subatomic particles located in electron orbitals around the nucleus; their mass is tiny, about 1/1840 the mass of a proton; charge or -1

Atoms have equal numbers of protons and electrons, their overall charge is zero (neutral)

ELEMENT – Matter containing only one type of atom. SYMBOL ATOMIC NUMBER The number of protons ATOMIC MASS The number of protons + neutron

ISOTOPES Atoms of the same element that have different numbers of NEUTRONS.

Chemical Bonds When two or more ELEMENTS chemically combined by bonding.

Chemical Bonds IONIC BONDS An attraction between atoms where electrons transferred

Ions A form of an atoms where electrons are either lost or gained. Ions have either a positive or negative charge.

Sodium Chloride (NaCl): An Ionic Bond

Chemical Bonds COVALENT BONDS Two atoms SHARE electrons (this forms very strong bonds). Example: Water (H2O) = 2 hydrogen + 1 oxygen MOLECULE – two or more ATOMS covalently bonded.

Water (H-O-H): A covalent bond

Properties of Water Water covers ¾ of Earth’s Surface Water is the single most abundant compound in most living things.

The Water Molecule Water has several important physical properties: It is a liquid at temperatures found over much of Earth’s surface. Water expands as it freezes. Water is more dense than ice, so ice floats. Which allows for fish and plant life to survive below the ice.

The Water Molecule Overall, water is a neutral molecule. However, a water molecule is polar. Although the entire molecule has equivalent numbers of protons and electrons, the electrons are unevenly distributed.

The Water Molecule The oxygen has a strong pull on the electrons near the oxygen making the probability of finding those electrons near the oxygen greater than finding them near the hydrogen atoms. This gives the oxygen end of the water molecule a slightly negative charge and the hydrogen ends of the water molecule a slightly positive charge. This uneven distribution of charge on a molecule is called polarity. When large numbers of water molecules get together, hydrogen bonding occurs.

Properties of Water COHESION – an attraction between molecules of the same substance. An example of cohesion is called surface tension- water molecules on the surface of a body of water cling tightly together and allow small organisms to survive on its surface. ADHESION – an attraction between molecules of different substances. Cohesion and adhesion work together to produce capillary action.

The water molecule ADHESION – an attraction between molecules of different substances. Cohesion and adhesion work together to produce capillary action. Adhesive forces cause the water to climb up the inside of the alls of the tubes, and cohesive forces allow the water molecules to cling to each other as it crawls up the tube.

Solutions and Suspensions

Solution and Suspensions Water is often found as a - a material composed of substances that are mixture two or more physically mixed together. Example: 1) Dissolving sugar into hot tea 2) Dissolving salt into hot water

Solution and Suspensions Two types of mixtures can be made with water: Solution – a mixture where a substance is evenly mixed in another substance. The substance in the smallest amount, which is is called the The substance in the greatest amount, which dissolved solute. dissolves the solute solvent.

Solution and Suspensions Water has the ability to dissolve many substances and thus is called the General Solubility Rule: universal solvent. - Like dissolves like Polar substances dissolve polar substances

MIXTURE – mixed but not chemically combined. SOLUTION – uniform mixture SOLVENT – dissolves other substances. SOLUTE – dissolves in the solvent. SUSPENSION – temporarily mixed

Acids, Bases, pH Water can react and divide/dissolve into two ions: H2O  H + OH Scientists have devised a scale to measure the amount of hydrogen ions that exist in solutions called pH. - +

Acids, Bases, pH The pH scale ranges from 0-14. When a solution has an equal number of H and OH ions such as water, it is assigned a neutral pH, which is 7 on the pH scale. When a solution has a high H concentration then it is assigned an acidic pH, which is a number less than 7 on the pH scale. When a solution has a low H concentration then it is assigned a basic pH, which is a number greater than 7 on the pH scale. + - - + +

Acids, Bases, pH The pH inside human cells must be kept close to neutral, between 6.5 and 7.5. If a chemical with a lower or higher pH enters the cell, it could disrupt chemical reactions there and thus disrupt the cell’s homeostasis.

Acids, Bases, pH Therefore, cells contain weak acids or bases called buffers which work to prevent changes in pH inside cells that are too acidic or too basic. For example, the skin has a surface film that is acidic and it acts as a buffer against strong bases like Clorox.