Journal Response Based on what you already know answer the following questions: What is an element? What is an atom? Write as much information down as you can think of.

Chapter 6: the Chemistry of Life

6.1 Atoms and their Interactions Elements A substance that can’t be broken down into simpler chemical substances Natural elements in living things Of the 90 naturally occurring elements, only 25 are essential to living organisms Carbon, hydrogen, oxygen, and nitrogen make up more than 96% of the mass of a human

Trace elements Some elements are present in very small amounts Iron Magnesium

Atoms: the Building Blocks of Elements Atom = the smallest particle of an element that has the characteristics of that element The structure of an atom All atoms have the same general arrangement The center of an atom is called the nucleus Protons: positive charge Neutrons: no charge Cloud around the nucleus Electrons: negative charge

Electron energy levels Electrons travel around the nucleus in certain regions known as energy levels Each energy level has a limited capacity for electrons Atoms contain equal numbers of electrons and protons No net charge

Isotopes of an Element Atoms of an element that have different number of neutrons in the nucleus Scientists refer to isotopes by giving the combined total of protons and neutrons in the nucleus

Quiz Name one of the four elements that make up 96% of human mass. What is the charge and location of an electron? Why do atoms have no net charge? Atoms of an element that have different number of neutrons are called ___? What is an atom?

Compounds and Bonding A compound is a substance that is composed of atoms of two or more different elements that are chemically combined

How covalent bonds form Atoms combine to become stable Are stable when the outermost electron energy level is full When two atom share electrons the force that hold them together is called a covalent bond

Most compounds in organisms have covalent bonds Sugars Fats Proteins Water A molecule is a group of atoms held together by covalent bonds and having no overall charge

How ionic bonds form An atom that gains or loses electrons has an electrical charge and is called an ion Ion = charged particle The attractive force between two ions of opposite charge is known as an ionic bond

Chemical Reactions When chemical reactions occur, bonds between atoms are formed or broken, causing substances to combine and recombine as different molecules All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism Reactions break down and build molecules that are important for the functioning of organisms

Writing chemical equations Substances that undergo chemical reactions are called reactants Substances formed by chemical reactions are called products The number before each chemical formula indicates the number of molecules of each substance The subscript number in a formula indicate the number of atoms of each element in a molecule of the substance Atoms are neither created nor destroyed in chemical reactions

Mixtures and Solutions When elements combine to form a compound, the elements no longer have their original properties A mixture is a combination of substances in which the individual components retain their own properties Do not combine chemically

A solution is a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent) In organisms, many vital substances, such as sugars and mineral ions, are dissolved in water The more solute that is dissolved in a given amount of solvent, the greater the solution’s concentration (strength) Organisms can’t live unless the concentration of dissolved substances stays within a specific range

Acids and Bases The pH is a measure of how acidic or basic a solution is A scale with values ranging from 0 to 14 is used to measure pH

Substances with a pH below 7 are acidic An acid is any substance that forms hydrogen ions (H+) in water Ex: Hydrochloric acid, lemon

Substances with a pH above 7 are basic A base is any substance that forms hydroxide ions (OH-) in water Ex: ammonia, eggs, drain cleaner

6.2 Water and Diffusion Water and Its Importance Water is perhaps the most important compound in living organisms

Water is polar Sometimes when atoms form covalent bonds, they do not share the electrons equally In a water molecule, the shared electrons are attracted more strongly by the oxygen atom than by the hydrogen atoms Polar molecule = a molecule with an unequal distribution of charge Has a positive end and a negative end Ex: water

Because of its polarity, water is able to creep up thin tubes Hydrogen bond = attraction of opposite charges between hydrogen and oxygen that forms a bond Because of its polarity, water is able to creep up thin tubes Plants use this: capillary action

Water resists temperature changes Water requires more heat to increase its temperature than do most other common substances Water is like an insulator that helps maintain a steady environment when conditions may fluctuate

Water expands when it freezes One of the few substances that expands when it freezes Ice is less dense than liquid water

Diffusion All objects in motion have kinetic energy Moving particles move in a straight line until it collides with another particle and both particles rebound. Particles of matter are in constant motion, colliding with each other.

Early observations: Brownian motion Robert Brown used a microscope to observe pollen grains suspended in water Noticed that the grains moved constantly in little jerks This motion is called Brownian motion The random motion of molecules and the resulting collisions

The process of diffusion Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration Results because of the random movement of particles A slow process because it relies on the random molecular motion of atoms

Three key factors affect the rate of diffusion Concentration = primary controlling factor The more concentrated the substances, the more rapidly diffusion occurs Temperature Increase in temperature causes more rapid movement and therefore speeds up diffusion Pressure Increasing pressure will accelerate molecular movement and therefore diffusion as well

The results of diffusion Diffusion will occur until the substance becomes equally distributed After this point the atoms continue to move randomly and collide with one another, but no further change in concentration will occur Dynamic equilibrium = condition of continuous movement but no overall concentration change

Diffusion in living systems Most substances in and around a cell are in water solutions where ions and molecules of the solute are distributed evenly The difference in concentration of a substance across space is called a concentration gradient If no other processes interfere diffusion will continue until there is no concentration gradient and dynamic equilibrium occurs

6.3 Life Substances Role of Carbon in Organisms A carbon atom has four electrons available for bonding Can form single, double, or triple bonds based on the number of electrons that are being shared When carbon atoms bond to each other they can form straight chains, branched chains or rings Compounds that have the same simple formula but different three-dimensional structures are called isomers

Molecular chains Some carbon compounds contain just one or two carbon atoms, whereas others contain tends, hundreds, or even thousands of carbon atoms Large molecules are called macromolecules A polymer is a large molecule formed when many smaller molecules bond together Condensation is the chemical reaction by which polymers are formed A water molecule is removed Hydrolysis is a method by which polymers can be broken apart A water molecule is added

The structure of carbohydrates A carbohydrate is an organic compound composed of carbon, hydrogen, and oxygen with a ratio of about two hydrogen atoms and one oxygen atom for every carbon atom The simplest type of carbohydrate is a simple sugar called a monosaccharide Ex: glucose, fructose

The largest carbohydrate molecules are polysaccharides Starch consists of highly branched chains of glucose units Used for food storage by plants Cellulose is another glucose polymer Forms the cell walls of plants

The structure of lipids Lipids are organic compounds that have a large proportion of C-H bonds and less oxygen than carbohydrates Commonly called fats and oils They are insoluble in water Molecules are nonpolar

The most common type of lipid consists of three fatty acids bound to a molecule of glycerol. Saturated fatty acid: contains only single bonds Cannot bond with any more hydrogen atoms Unsaturated fatty acid: contains single, double, and possibly triple bonds Can bind with more hydrogen atoms

The structure of proteins Proteins are essential to all life Provide structure for tissues and organs and carry out metabolism A protein is a large, complex polymer compound of carbon, hydrogen, oxygen, nitrogen, and usually sulfur

The basic building blocks of proteins are called amino acids 20 common amino acids The covalent bond formed between the amino acids is called a peptide bond The number and order of amino acids in protein chains determine the kind of protein An enzyme is a protein that changes the rate of a chemical reaction Increase the speed of reactions

The structure of nucleic acids A nucleic acid is a complex macromolecule that stores cellular information in the form of a code Made of smaller subunits called nucleotides Consist of carbon, hydrogen, oxygen, nitrogen, and phosphorus atoms arranged in three groups; Base Simple sugar Phosphate group

RNA (ribonucleic acid) forms a copy of DNA DNA (deoxyribnucleic acid) is the master copy of an organism’s information code Determines how an organisms looks and acts RNA (ribonucleic acid) forms a copy of DNA