Textbook Chapter 2 Flashcards
Matter definition
Organisms are composed of matter, which is anything that takes up space and and has mass. Matter exists in many forms. Rocks, metals, oils and gases and living organisms are examples of matter.
Element defintion
Matter is made up of elements. An element is a substance that cannot be broken down down into other substances by chemical reactions. Today there are 92 recognized elements occurring in nature.
Compound definition
A compound is a substance that consists of two or more different elements in a fixed ratio. Table salt or NaCl has a fixed ratio of 1:1. Water of H2O consists hydrogen and oxygen in a 2:1 ratio. These simple examples are examples of organized matter having emergent properties, compounds have different properties than elements.
Essential elements for life
Of the total 92, only 20-25% are essential elements that an organism needs to live a healthy life and reproduce. The essential elements are similar among organisms but there is variation. Humans need 25 however plants only need 17.
Oxygen, Hydrogen, Nitrogen and Carbon make up 96% of living matter.
Trace elements
Ca, P, K, S and a few other elements account for the missing 4% of an organism’s mass. Trace elements are only required in minute quantities in an organism. some like iron (Fe) are required by all life forms, others are only required by certain species. Iodine for example is only required in vertebrates.
Element properties and atoms
Each element consists of atoms that are different from the atom of any other element. An atom is the smallest unit of matter that still retains the properties of an element.
Concept 2.1: Matter consists of chemical elements in pure form and in combinations called compounds
Elements cannot be broken down chemically to other substances. A compound contains two or more different elements in a fixed ratio. Oxygen, carbon, hydrogen, and nitrogen make up approximately 96% of living matter.
Concept 2.2: An element’s properties depend on the structure of its atoms
An electrically neutral atom has equal numbers of electrons and protons; the number of protons determines the atomic number. The atomic mass is measured in daltons and is roughly equal to the mass number, the sum of protons plus neutrons. Isotopes of an element differ from each other in neutron number and therefore mass. Unstable isotopes give off particles and energy as radioactivity.
■ In an atom, electrons occupy specific electron shells; the electrons in a shell have a characteristic energy level. Electron distribution in shells determines the chemical behaviour of an atom. An atom that has an incomplete outer shell, the valence shell, is reactive.
■ Electrons exist in orbitals, three-dimensional spaces with spe- cific shapes that are components of electron shells.
Concept 2.3: The formation and function of molecules depend on chemical bonding between atoms
Chemical bonds form when atoms interact and complete their valence shells. Covalent bonds form when pairs of electrons are shared.
Molecules consist of two or more covalently bonded atoms. The attraction of an atom for the electrons of a covalent bond is its electronegativity. If both atoms are the same, they have the same electronegativity and share a nonpolar covalent bond. Electrons of a polar covalent bond are pulled closer to the more electronegative atom, such as the oxygen in H2O.
An ion forms when an atom or molecule gains or loses an elec- tron and becomes charged. An ionic bond is the attraction be- tween two oppositely charged ions.
Weak interactions reinforce the shapes of large molecules and help molecules adhere to each other. A hydrogen bond is an attraction between a hydrogen atom carrying a partial positive charge (d+) and an electronegative atom (d-). Van der Waals interactions occur between transiently positive and negative regions of molecules.
A molecule’s shape is determined by the positions of its atoms’ va- lence orbitals. Covalent bonds result in hybrid orbitals, which are responsible for the shapes of H2O, CH4, and many more complex biological molecules. Shape is usually the basis for the recogni- tion of one biological molecule by another.
Concept 2.4: Chemical reactions make and break chemical bonds
Chemical reactions change reactants into products while conserving matter. All chemical reactions are theoretically reversible. Chemical equilibrium is reached when the forward and reverse reaction rates are equal.
