1Living organisms are composed of MATTER, which is anything that occupies space and has mass.An ELEMENT is a substance that cannot be broken down to other substances by ordinary chemical means. TRACE ELEMENTS- essential but only in minute quantities.The four most abundant elements in the human body are Carbon, Oxygen, Hydrogen, and Nitrogen.2Goiter in a Malaysian woman, a symptom of Iodine deficiency. 3A COMPOUND is a substance consisting of two or more different elements combined in a fixed ratio. Pure sodium is a metal and pure chlorine is a poisonous gas, but when chemically combined they make the compound sodium chloride an edible compound used daily.4An ATOM is the smallest unit of matter that still retains the properties of an element.Atom’s have 3 important subatomic particles: 1.) PROTON is a subatomic particle with a single positive charge(+)2.) ELECTRON is a subatomic particle with a single negative electrical charge (-)3.) NEUTRON is electrically neutral (has no electrical charge)The NUCLEUS of an atoms houses NUETRONS and PROTONSElements differ in the number of subatomic particles in their atoms. All atoms of a particular element have the same unique number of protons. The number of protons that an atoms has is called the ATOMIC NUMBER.The atom’s MASS NUMBER is the sum of the protons and neutrons in its nucleus.5ISOTOPES- An element have the same numbers of protons and electrons and behave identically in chemical reactions, but they have different numbers of neutrons.RADIOACTIVE ISOTOPES- is one in which the nucleus decays spontaneously, giving off particles and energy. 6Basic research- Biologist often use radioactive tracers to follow molecules as they undergo chemical changes in a organism. Medical Diagnosis- By injecting a radioactive chemical into a patient’s blood and then measuring the amount of radioactive material passed in the urine. Radioactive tracers are often used for diagnosis in combination with sophisticated imaging instruments like the image above. Dangers- Though radioactive isotopes have many beneficial uses, uncontrolled exposure to them can harm living organisms by damaging molecules, especially DNA. The particles and energy thrown off by radioactive atoms can break chemical bonds and also cause abnormal bonds to form.7Only electrons are directly involved in the chemical activity of an atom. Electrons vary in the amount of energy they possess. The farther an electron is from the nucleus , the greater its energy. Electrons occur only at certain energy levels, called ELECTRON SHELLS. It is the number of electrons in the outer most shell that determines the chemical properties. When two atoms with incomplete outer shells react, each atom either shares, donates, or receives outer electrons, so that both partners end up with completed outer shells. These interactions usually result in atoms staying close together, held by attractions known as CHEMICAL BONDS.8ION- is an atom or molecule with an electrical charge resulting from a gain or loss of one or more electrons. Two ions with opposite charges attract each other: when the attraction holds them together, it is called an IONIC BOND, also known as a salt.9The second type of strong chemical bond is the COVALENT BOND, in which two atoms share one or more pairs of outer-shell electrons. Two or more atoms held together by covalent bonds form a MOLECULE. H2, called the molecular formula, tells you that the molecule consists of two atoms of hydrogen. The line between the hydrogen atoms represents the single covalent bond formed by the sharing of a pair of electrons. DOUBLE BONDS form when atoms share two pairs of electrons.10Atoms in a covalent bonded molecule are in a constant tug-of-war for the shared electrons of their covalent bonds. An atom’s attraction for shared electrons is called its ELECTRONEGATIVITY. The more electronegative an atom, the more strongly its pulls shared electrons towards its nucleus. In NONPOLAR COVALENT BONDS- electrons are shared equally between the atoms. The unequal sharing of electrons produces a POLAR COVALENT BOND, which is the pulling of shared, negatively charged electrons closer to the more electronegative atoms makes that atom partially negative and the other atom partially positive. POLAR MOLECULES- has an unequal distribution of charges.11Large molecules are held in their three-dimensional shape by weak bonds. In addition, molecules in a cell may adhere briefly by weak bonds, respond to one another in some way, and then separate. When a hydrogen atom is part of a polar covalent bond, its partially positive charge allows it to share attractions with other electronegative atoms. Because the positively charged region in this special type of bond is always a hydrogen atoms, the bond is called a HYDROGEN BOND. You will learn how hydrogen bonds help to create a proteins shape (and thus its function) and hold the two strands of a DNA molecule together. Indeed, these weak bonds are involved in many of the activities of a cell.12Cohesion in water is much stronger for water than for most other liquids. The veins of trees use the strong cohesion of water molecules to pull it against gravity. Adhesion helps the water molecules to ride on the cell walls of the veins.Cohesion: The tendency of molecules to stick togetherAdhesion: The clinging of one substance to anotherSurface tension: A measure of how difficult it is to stretch or break the surface of a liquid 13Because of hydrogen bonding, water has a better ability to resist temperature change than most other substances. HEAT- is the amount of energy associated with the movement of atoms and molecules in a body of matter.TEMPERATURE- Measures the intensity of heat- that is, the average speed of molecules rather than the total amount of energy in a body of matter.Heat must be absorbed in order to break hydrogen bonds, and heat is released when hydrogen bonds form. Water moderates internal temperatures by evaporative cooling. When a substance evaporates, the surface of the liquid remaining behind cools down as the molecules with the greatest energy leave.14Water exists in nature as a gas, liquid, and solid. As water freezes, each molecule forms stable hydrogen bonds with four neighbors, holding them at arms length and creating a 3D crystal. Compare the specially arranged molecules in the ice crystal with the more tightly packed molecules in the liquid water.15A SOLUTION is a liquid consisting of a uniform mixture of two