Structure Of Atoms O Different Elements example essay topic

Chapter 4 The Chemical Basis of Life Introduction o Your body is an elaborate chemical system. o Chemical signals between brain less enable your mind to understand what you see. o You nourish those cells with chemicals that are obtained from food. o Life is all about chemicals and how they interact Concept 4.1 Life requires about 25 chemical elementsElementso Humans and other organisms are examples of matter. Matter: Anything that occupies space and has mass. (Physical things) o The various forms of matter are composed of one or more chemical elements. Element: A pure substance that cannot be broken down into smaller substances by chemical mean so There are 25 elements are essential to life.

Four of these elements are Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N). These make up about 96% of the living matter in your body. Calcium (CA), Phosphorus (P), Potassium (K), sulfur (S), and a few other elements account for most of the remaining 4%. Trace Elements: elements that make up less that 0.01 percent of your body mass are nevertheless critical to your health. Compounds Most elements can interact with other elements forming complex types of matter called compounds. Compound: A substance containing two or more elements that are chemically combined in a fixed ratio. o Compounds properties may differ greatly from those of its components. o Though simple compounds like sodium chloride and water play important roles in living things, most compounds found in organisms are more complex, containing at least three or four elements.

Concept 4.2 Chemical properties are based on the structure of atoms. o Different elements have different properties. o Some are solid metal at room temperature, some are invisible gases, some elements readily react with other elements, whiles others hardly react at all. o These properties affect the roles that different elements play in biological processes. This section describes how an elements properties to its structure. Atoms Each element consists of a single kind of atom that is different from the atoms of all other elements. o Atom- gets its name from the Greek word atoms, meaning "indivisible" is the smallest possible "Pierce"-it would take more than tree million carbon atoms to stretch across the period printed at the end of this sentence. o Atoms are all elements are made up of even smaller components called subatomic particles. Proton: Is a subatomic particle with a single unit of positive electrical charge. Electron: is a subatomic particle with a unit of negative charge.

Neutron: is electrically neutral. Nucleus: is the center of an atom. It is made up of tightly packed protons and neutrons. o Electrons, which have much less mass than neutrons and protons continually, move about the outside of the nucleus at great speed. o The attraction between the negatively charged electrons and the positively charged prop ones keeps the electrons close to the nucleus o An important difference among elements is the number of protons in their atoms. o All atoms of a particular element have the same number of protons known as the elements atomic number. o Left alone, An atom tends to hold as many electrons as protons o In that state, an atom is electrically neutral the positive charges on the protons exactly balance the negative charges. However, the numbers of electrons is not constant like the number of protons. o The number of electrons determines how the atom interacts with other atoms. No two elements have the same atomic number (proton number) so no two elements have the same chemical behavior.

Isotopes Some elements have alternate forms called Isotopes. Isotope: An element with the same number of protons, but different number of neutrons. Radioactive Isotope: When the nucleus breaks down, or decays in an isotope, it gives off radiation in the form of matter and energy. This is then known as a radioactive isotope. o Radioactive isotopes have many uses in research and medicine. Living cells use radioactive isotopes just as they would use the non radioactive forms. They are then useful as "biological spies" for observing what happens to different atoms within organisms. o The particles and energy they give off can damage cells. o Most doses that are used in medical science however are safe.

Electrons and Reactivity o The electrons determine how much an atom will react with others. o Elements differ in the amount of energy they have and how tightly they are held by the protons in the nucleus. Based on these properties chemists describe an atoms electrons as belonging to certain level of an atom that determines how that atom reacts. o The first level (nearest the nucleus) can hold 2 electrons while the second energy level can hold 8 electrons. o In the next section you will read more about the ways electrons are involved in the reaction among atoms.