How Matter is Organized All living things consist of matter. Matter is anything that occupies space. mass is the amount of matter in any object. weight is the force of gravity acting on matter. In outer space, weight is close to zero, but mass remains the same as on Earth. States of matter Solid – has definite shape and volume Liquid – has definite volume, changeable shape Gas – has changeable shape and volume

The Organization of Matter An element is a pure substance that can’t be broken down into simpler substances by ordinary chemical or physical techniques All matter (anything that occupies space and has mass) is composed of elements and combinations of elements Ninety-two different elements occur naturally on Earth – other artificial elements have been synthesized in the laboratory

Common Elements in Living Organisms

Elements found in biological molecules

Atomic Structure Each element consists of one type of atom Each atom consists of an atomic nucleus surrounded by fast-moving, negatively-charged electrons Atomic nuclei contain positively charged protons – the number of protons (atomic number) identifies an element The nuclei of all atoms (except hydrogen) also contain uncharged neutrons

Atomic Structure

Atomic Number and Mass Number Atomic number = # protons Each element has its own number of protons Carbon has 6 protons. Oxygen has 8. If you change the number of protons you change the element If you add another proton to carbon it will have 7 which makes it nitrogen Mass = # protons + # neutrons Different masses of the same element are called isotopes (isotopes differ in # of neutrons; unstable isotopes decay and emit particles until they are stable, they are radioactive isotopes)

Isotopes of Carbon

Focus On Applied Research Scans of human thyroid glands after iodine-123 was injected into the bloodstream Radioactive iodine becomes concentrated in the thyroid gland

Compounds Molecules whose component atoms are different (such as carbon dioxide) are called compounds The chemical and physical properties of compounds are typically distinct from those of their atoms or elements Example: Hydrogen (H) and oxygen (O) – the elements that form liquid water (H2O) – are both highly flammable gases

Electron Shells Within an atom, electrons are found in regions of space called energy levels or shells Maximum # of electron in a shell: 2n2 (‘n’ is the number of shell; n = 1, 2, 3, 4…….) The arrangement of electrons in the shells is known as electronic configuration of an atom. Sodium has 11 electron; so the electronic configuration of a carbon atom is 2, 8, 1 Chlorine has 17 electron; so the electronic configuration of a carbon atom is 2, 8, 7

Chemical Bonds and Chemical Reactions The three most important chemical linkages in biological molecules are ionic bonds, covalent bonds, hydrogen bonds. Chemical reactions occur when atoms or molecules interact to form new chemical bonds or break old ones Ionic bonds result from electrical attractions between atoms that gain or lose valence electrons completely A positively charged ion (one that has lost an electron), such as Na+, is called a cation A negatively charged ion (one that has gained an electron), such as Cl--, is called an anion

Formation of an Ionic Bond

Covalent Two atoms share their outer electrons forming a bond H2O, CO2, NH3, O2 are held together by covalent bonds

Intermolecular Forces Polar molecules have a slightly positive end and a slightly negative end Polar molecules form weak polar bonds with other polar molecules Polar molecules containing hydrogen will form hydrogen bonds with other polar molecules. Water is a polar molecule.

Water is important to life Forms hydrogen bonds with itself and other polar molecules (Hydrophilic) Forms a solution for many chemical reactions inside our cells Moderates temperature Required for photosynthesis

Inorganic Compounds & Solvents Most of the chemicals in the body are compounds Inorganic compounds usually lack carbon & hydrogen and are structurally simple water, carbon dioxide (a by-product of cell metabolism), oxygen (important in metabolic reaction,) acids, bases and salts Organic compounds contain carbon & hydrogen always have covalent bonds

Water Water makes up about 2/3 of total body weight. Aqueous solution containing +/- ions will conduct electrical current. + & - move toward each other. Homogenous mixture of two or more substances is called, solution. The medium in which other atoms, ions molecules are dispersed is called the solvent. The dispersed substances are the solute. When water is the solvent, the solution is known as aqueous solution.

Acids and Bases Acids are proton donors that release H+ (and anions) when they are dissolved in water, increasing the H+ concentration Example: Hydrochloric acid (HCl) dissociates into H+ and Cl– when dissolved in water (HCl ↔ H+ + Cl– ) Bases are proton acceptors that reduce the H+ concentration of a solution; most release a hydroxide ion (OH–) and a cation Example: NaOH → Na+ + OH– ; excess OH– combines with H+ to produce water (OH– + H+ → H2O)

pH Acids are molecules that give up a positive hydrogen ion (H+) The concentration of H+ ions in a water solution, compared with the concentration of OH– ions, determines the acidity of the solution Acidity is measured using the pH scale: ranging from 0 to 14 – based on logarithms of the number of H+ ions in solution: pH = –log10[H+] Acids are molecules that give up a positive hydrogen ion (H+) Bases are molecules that accept a positive hydrogen ion (H+) How readily an atom accepts or donates a hydrogen is indicated by its pH Acids - 0 < pH < 7 Bases - 7 < pH < 14 Water pH = 7 (Neutral)

pH Scale

Buffer Systems of the Body Body fluids vary in pH but the range of each is limited and is maintained by a variety of buffering systems. gastric juice 1.2 to 3.0; saliva 6.35 to 6.85; bile 7.6 to 8.6 and blood 7.35 to 7.45 Buffer: that resists the change in pH Buffers stabilize the pH of a solution by removing or replacing hydrogen ions. carbonic acid - bicarbonate buffer system

TYPES of chemical reactions Decomposition AB A + B Synthesis A + B  AB Exchange AB + CD  AC +BD HCl + NaHCO3  H2CO3 + NaCl Decomposition- catabolism, breaking molecules in two or more substances; usually exergonic, releases heat. All the synthesis reactions in the body together are called anabolism Two or more atoms, ions or molecules combine to form new & larger molecules Usually are endergonic because they absorb more energy than they release