Particle Charge Mass Location Proton + 1 In nucleus Neutron O 1 In nucleus Electron -- Small fraction of proton 1/1837

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1 ATOM UNIT NOTES: Building Blocks of Matter: The atom is the smallest piece that keeps the properties/characteristics of that type of particle. They are the building blocks of matter. Atoms are made of protons, neutrons, and electrons. If the atom is broken down to the smaller pieces, then it loses the characteristics of that type of atom. A certain combination of protons, neutrons, and electrons make one type of atom with characteristics found only in that type of atom. This is an element. The smaller pieces are in certain locations and may or may not have an electrical charge. They also have mass since they are made of matter. The nucleus is the small dense area in the center of the atom where protons are located. The electrons circle outside the nucleus in an electron cloud. Particle Charge Mass Location Proton + 1 In nucleus Neutron O 1 In nucleus Electron -- Small fraction of proton 1/1837 Electron cloud outside nucleus The atomic number is the number of protons. If this number changes then so does the type of atom/element. There are 92 natural elements. Others in the Periodic table are man-made. The 6 most common elements in life are P, H, O, N, C, S. Since protons are positive, an equal number of electrons will balance out the atom and make it neutral. The atomic number then tells the number of electrons too. To find the number of neutrons, subtract the number of protons from the atomic mass. Usually the number will round up the number if it is above 0.5. Round down if it is below 0.5. Knowing how an element is structured can help explain how it functions and react with other elements. There are different energy levels for the electrons outside the nucleus in the cloud. Electrons move so fast they cannot be pinpointed

2 to a certain place at any time, but can be placed in an orbit. A model of the atom with energy levels was proposed by Niels Bohr. The energy levels are also called valences. The electrons in the outer shell are called valance electrons. These are the ones that are available to bond with other electrons in other atoms. Energy levels: 1 st holds 2 electrons 2 nd holds 8 electrons 3 rd holds 8 electrons 4 th hold 18 electrons 5 th holds 18 electrons etc. There are also Electron-dot diagrams proposed by Lewis. They show only the valance electrons that are available to bond with other atoms.

3 Isotopes: There are atoms of the same element that have the same number of protons, but differ in the number of neutrons. This is similar to cars that have slightly different features but are all the same model. Isotopes are usually unstable and radioactive. Isotopes can be written by their symbol and their mass number. i.e. C12 is the normal form of Carbon, but C14 is a radioactive isotope. C12 has 6 protons and 6 neutrons, but C14 has 6 protons and 8 neutrons. How to read the Periodic Table: The rows are called periods that show the number of valence levels, while the columns are families or groups that show the number of valence electrons in the outermost valence shell. The shape of the table reflects the number of elements that meet both the number of electrons and the energy level. There are two elements in the first period (row) since there are only two electrons in the first valence shell or energy level. There are 8 elements in the next period (row) since 8 electrons can fit in the 2 nd energy level. And so on. The elements on the left are the most reactive, while those on the right are the least reactive. These on the right are called noble gases because have their valence shells or energy levels full.

4 Molecules, Compounds, and Ions: Molecules are a group of two or more atoms/elements that can be the same or different. These atoms are chemically bonded together. For example, H2 is H H CO2 is O=C=O Compounds are formed when 2 or more different atoms/elements which are chemically bonded. A compound s properties are always different than the elemental properties that come together to make the compound. For example, H2O has 2-H + 1-O H2O Use formulas or models to show what elements are in the compound and how many there are in the molecule/compound: Molecular formula: CO2 H2O Structural formula: O=C=O Space filling model: Ball and stick model: Mixtures are two or more substances that are physically combined but NOT chemically. They are held together by physical forces. They can be separated easier and with less effort than chemically combined compounds. When they are separated, the components are not destroyed. If the parts of a compound are separated, then the compound will be destroyed and take more energy/effort to do so. For example: salad, soil, gorp. An Ion is an atom (or groups of atoms in a molecule or compound) that is electrically charged because of the gain or lass of one or more electrons. When an atom loses and electron, it then has a positive (+) charge. When an atom gains an electron, ot then has a negative (-) charge. A positive ion is called a cation (+) and a negative ion is an anion (-). An atom s nucleus never changes during the gain or loss of electrons to form an ion. The formationof an ion is called ionization. The chemical properties of an ion depend on the electron arrangement which is based on the number of electrons. For example, an ion has more or less reactivity, electron affinity. This can also be thought of as its potential to gain or lose electrons. An ion creates a different electron configuration (or shape) with more or less electrons which changes its chemical properties too. Ions can combine with other ions to make new compounds because the ions have electrical charges, either positive or negative. Opposite charges will attract. For example, Na+ and Cl- combine to make Na+Cl-. Na and Cl by themselves are harmful to humans but when they combine they make a new substance that is useful, table salt. The ion form of the element can be beneficial when the normal would have been dangerous. For example, Li is dangerous to humans, but Li+ is used to treat mental disorders.

5 Types of Chemical Bonds: A bond involves 2 electrons, one from each atom involved. Atoms like to have their outer valence shell full. They can make as many bonds as it takes to fill the shell. This is called the Octet Rule. Sometimes the bond can be double or triple to make this happen. This means two atoms will share two or three pairs of electrons. For example, oxygen needs two more electrons to fill its outer valence shell and hydrogen needs one to fill its valence shell. H2O is the result of that number of electrons. Oxygen bonds two electrons, one from each hydrogen, and hydrogen gets its last electron from oxygen. They all now have a filled outer valence shell. Covalent bonds are when atoms share electrons. The sharing can be equal or unequal. When sharing is equal the atom travels in both atoms an equal amount of time so the charge is equally spread out. This is a nonpolar covalent bond since no charged poles are created. This type of bond happens in substance like oil. Unequal sharing is when the electron spends more time with one atom than the other and creates slightly charged poles. The atom that the electron is with more will be slightly negative and the atom that has less time with the electron will be slightly positive. This is a polar covalent bond. For example, water. Covalent bonds are between two nonmetals. The periodic table above shows where the metals and nonmetals are. For example, H and O makes H2O Water is the universal solvent which can have the most number of other substances dissolve in it, but nonpolar substance like oil will not dissolve in polar substance. Ionic bonds When an atom only has 1,2, or sometimes 3 electrons in its outer valence shell, it is more likely to lose them to another atom that needs to fill 1,2, or 3 electron spots in its valence shell. The fewer electrons in the shell, the more likely they will be lost to another atom that needs them to fill its 1 or 2 spots. Once electrons are gained or lost, the atom has a slight charge which can then attract the opposite charge and form a weak bond. They are not sharing electrons but are held together only by the attraction of opposite charges like in a magnet. For example, The ionic bond is weaker than the covalent bond. The structure of ionic substance will be in a lattice form. Ionic bonds are between 1 metal and 1 nonmetal, such as Na and Cl.

6 Atomic Theory vs. Scientific Theory: The Atomic Theory explains the structure and behavior of the atom. It took hundreds of years to develop since the idea of the atom was first proposed by Democritus. The following scientists were involved in the discovering the structure and thus behavior of the atom. The work of some were validated by those that followed and the work of some were proven incorrect. But that is the purpose and process of a scientific theory. As scientists discover new things, new facts, new information, previous findings will hold true or not. That does not mean the scientist was a crackpot or a bad scientist, but that his work was not correct. Science is a process of discovery. If the information is right or wrong, it is still helpful. Democritus ( BC) Aristotle ( BC) Johann Becher ( ) George Stahl ( ) Joseph Priestly ( ) Antoine ( and Marie) Lavoisier ( ) Joseph Proust ( ) John Dalton ( ) Joseph Gay-Lussac ( ) Amadeo Avagadro ( ) Stanislao Cannizzaro ( ) Dimitri Mendeleev ( ) J.J. Thomson ( ) Ernst Rutherford ( ) Niels Bohr ( ) Henry Moseley ( ) Francis Aston ( ) Erwin Schrodinger ( ) Werner Heisenberg ( ) James Chadwick ( ) **We will do a class project to discover more about each of these scientists and their contribution to the Atomic Theory. Comparing the Atomic Theory to a general scientific theory Difference Similarity Difference One topic *Started with observations *Developed a testable hypothesis *Conducted one or more experiments *Published their work *It was peer reviewed *Validated or not Many topics possible