The Nature of Matter Chapter 2 Section 1

Objectives  Identify the three subatomic particles found in atoms  Explain how all of the isotopes of an element are similar and how they are different  Explain how compounds are different from their component elements  Describe the two main types of chemical bonds

Important Vocabulary  Atom  Nucleus  Electron  Element  Isotope  Compound  Ionic bond  Ion  Covalent bond  Molecule  van der Waals forces

What are you made of?  Earth supports an enormous variety of organisms  The structure and function of all living things are governed by laws of chemistry  All living things are made of the same basic materials: carbon, hydrogen, oxygen, and nitrogen  To understand biology we must also understand the chemistry of life

History of Atoms  The study of chemistry begins with the basic unit of matter, the atom  The idea of the atom first came from a Greek philosopher Democritus nearly 2500 years ago  It started with a set of simple questions, “If you take a piece of chalk and break it in half, are both halves still chalk? If you continue to divide each piece, is there a limit to the division before it becomes something else?”  Democritus thought there was a limit which he called atomos, meaning “unable to be cut”

Characteristics of Atoms  Are incredibly small  Made of three subatomic particles  Protons  Electrons  Neutrons

Protons & Neutrons  Located in the center of an atom in a structure known as the nucleus  Protons are particles with a positive charge  Neutrons are particles with no charge  Strong forces bind protons and neutrons together

Electrons  Electrons are negatively charged particles  Have very high energy and very little mass (1/1840 of a proton)  They are in constant motion outside of the nucleus  They are attracted to the protons in the nucleus but remain outside because of their energy of motion  Atoms have equal numbers of protons and electrons, so that their charges balance out, making them electrically neutral

Model of the Atom

Elements  An element is a pure substance that consists entirely of one type of atom  118 elements are known  114 elements have official names as of 2014  Only about two dozen are commonly found in living organisms  They are represented by 1-2 letter symbols and contained in the Periodic Table  The atomic number of each element tells the number of protons in its nucleus

Reading the Periodic Table

Isotopes  Isotopes are atoms of an element that have different numbers of neutrons  The total number of protons and neutrons in an atom is given by the mass number  Elements are made up of a mixtures of isotopes so their atomic mass is a weighted average of all the element’s isotopes  Because the number of electrons is the same for all the isotopes of an element, all isotopes of one element have the same chemical properties

Isotopes of Carbon Carbon-12 Carbon-13Carbon-14

Radioactive Isotopes  Some isotopes are radioactive, which means that their nuclei are unstable and break down at a constant rate over time  The radiation these isotopes give off can be dangerous, however they are still often used for important scientific, medical and practical uses  For example:  Geologists use them to date the age of rocks  Some radiation from isotopes is used to treat cancer or kill bacteria  Some isotopes are used as tracers to follow the movement of substances within living organisms

Compounds  Most elements do not exist alone  They easily combine with the same or different atoms of elements  Compounds are substances of 2 or more elements combined in fixed proportions  Compounds are unique, their physical and chemical properties are different from the elements that form them  A chemical formula shows the kinds and proportions of atoms of each element in the compound  For example: Fe 2 O 3  2 iron atoms and 3 oxygen atoms

Chemical Bonds  Atoms in compounds are held together by various types of chemical bonds  Bond formation involves the electrons of atoms  The electrons available to form bonds are called valence electrons  There are two main types of chemical bonds:  Ionic  Covalent

Ionic Bonds  Are formed when one or more electrons are transferred between atoms  An atom that loses electrons becomes positively charged  An atom that gains electrons becomes negatively charged  These charged atoms are called ions

Ionic Bond  Example: NaCl = sodium chloride

Covalent Bonds  Form when 2 atoms share one or more pairs of electrons  When 1 pair of electrons is shared, it’s a single covalent bond (2 electrons shared)  When 2 pairs of electrons are shared, it’s a double covalent bond (4 electrons shared)  When 3 pairs of electrons are shared, it’s a triple covalent bond (6 electrons shared)  The result of a covalent bonding is a molecule  Molecules are the smallest unit of most compounds

Single Covalent Bonds

Double Covalent Bonds

Triple Covalent Bonds

van der Waals Forces  Some atoms have stronger attractions for electrons than do other atoms  When the atoms in a covalent bond share electrons, the sharing is not always equal  Even when the sharing is equal, the rapid movements of electrons can create regions on a molecule that have tiny positive or negative charges  When molecules are close together, a slight attraction can develop between oppositely charged regions of nearby molecules  These intermolecular forces are called van der Waals forces  They are generally weak bonds

Elements Isotopes Different # of neutrons Compounds Ionic bonds Ions Atoms Protons Neutrons Electrons Molecules Covalent bonds