The Atom: basic unit of all matter The Atom is composed of many small particles. We are going to concentrate on the THREE MAIN ONES: •Inside the nucleus there are TWO ……the Proton (has a positive charge) and the Neutron (neutral) •Outside of the nucleus, roams the electron (has a negative charge) The Nucleus: The central core of the atom. Provides the mass of the atom. Has an overall positive charge due to the protons within. Mass number: the number of protons + the number of neutrons Atomic number: the number of protons You should notice that each has its own number of proton(s) and thus, an equivalent number of electrons, since all atoms are neutral until they react with another. # of protons electrons # of = Determining an Atom’s Mass Number and Atomic Number by Using the Periodic Table 7 N 14.00674 Atomic Number Element’s symbol Relative Atomic Mass What about that Mass NUMBER??????? So, from the periodic table you can determine the number of protons since it is the same as the atomic number. But, how do you determine the number of neutrons? Well, remember the definition of isotopes? Each atom has at least two isotopic forms. So, we have two ways to determine the number of protons for an individual atom. First, from a special symbol, like the C-14 or C-12. The 14 and the 12 are the given mass numbers for that atom. So, given this info, all you have to do is: Remember the mass number = #p + #n and, so mass number - #p = # neutrons #14 - 6p = 8 neutrons and #12 - 6p = 6 neutrons You try some: Li -7: #p = ____, # e = _____, # n = ____ P- 31: #p = ____, # e = _____, # n = ____ Pb-207: #p = ____, # e = _____, # n = ____ Cl-35: #p = ____, # e = _____, # n = ____ Answers: Li-7 has 3 protons, 3 electrons, 4 neutrons P-31 has 15 protons, 15 electrons, 16 neutrons Pb-207 has 82 protons, 82 electrons, 125 neutrons Cl-35 has 17 protons, 17 electrons, 18 neutrons If you are not given this symbol with the mass number, you can still determine the mass number for the most abundant isotopic form for that atom. For example, if you look on the periodic table for Carbon, you will see a value underneath its symbol - the RELATIVE ATOMIC MASS of 12.011. This mass is a special average mass for all of the isotopes that exist for that atom. It takes into consideration HOW abundant each isotope is. So, the most abundant isotope has the most influence on this mass! So, if you round this number to the nearest whole number you have the MASS NUMBER FOR THE MOST COMMON ISOTOPE. A few examples, determine the #p, #e, #n: 53 16 13 I S Al 32.066 26.981539 126.90447 Answers: Iodine has 53 protons, 53 electrons, 74 neutrons Sulfur has 16 protons, 16 electrons, 16 neutrons Aluminum has 13 protons, 13 electrons, 14 neutrons More on those electrons!!! Electrons exist outside of the nucleus, are extremely small and so are nearly weightless, and move at the speed of light!!!!!! So, they do not add much to the mass of the atom but they do control the chemical activity of the atom and the SIZE of the atom because of all that motion. Electron Clouds Electrons are moving constantly. So, it is impossible to know, at any given moment, their exact position. So, we say that they exist in a region of space known as the electron cloud. Since electrons are negative they want to get close to the positive nucleus. But, since negative repels negative, electrons have to arrange themselves in special orbits called energy levels. They do this in order to be close to the positive nucleus yet, not repelling each other too much. Shapes of the Electron Clouds Energy Levels The first energy level can only hold up to TWO electrons to be STABLE. The second energy level can hold up to EIGHT electrons. The third can hold up to 18 electrons. This can be determined by using the following formula: 2(n2) ; where the n = energy level # So, what could the 4th hold?____the 5th?___ Valence electrons – outermost electrons from the nucleus *Most atoms want to have 8 valence electrons because it is the most stable configuratiion!!!! (The Great Eight = an octet) Only the simplest of atoms can be realistically drawn. Drawing an atom of Fluorine (F-19) e- ee- ____#protons ____# electrons ____#neutrons e- e-e- e-e- e- How many electrons would fluorine like to get, to be stable?__________ e- e- Number of Valence Electrons in a Family 1e 2e 3e 4e 5e 6e 7e 8e Draw an atom of: hydrogen(H-1) oxygen (O-16) e- e- e- hydrogen (H-1) e- ee- e- ee- e- Let’s bond these 2 hydrogen and 1 oxygen together to make ………. e- ee- ee- e- Partial charges should be drawn on water since it is polar. More on this later! e- ee- e- We just created a COVALENT BOND. This is a bond in which two or more atoms SHARE electrons so that they all become more stable. Ionic Bonding Some elements do not want to share electrons because their nucleus is so strong it actually takes the electrons from another atom. This strong atom which GAINS electrons (which are negative) becomes a NEGATIVEcharged ION, OR ANION. Ion: an atom that has lost or gained ELECTRONS! The weaker atom, which loses an electron or more, becomes a POSITIVE-charged ion, a CATION. Once these atoms become IONS, they are now attracted to one another and so you have what is called an IONIC BOND. Diagram of what happens in an Ionic Bond Draw a sodium (Na) e- eeeeeeeee- Draw a chlorine (Cl e- e- e- ee- e- e- eeee- eeeeeeeeee- Once done, charges should be drawn in since you no longer have neutral atoms but IONS! Ionic Bonds and Cations What would be easier (require less energy)? To give away 1 or 2 electrons or bring in 6 or 7 electrons in order to gain that octet? So: Metals are found on the left side of the periodic table. Metals in column 1 have only one valence electron and in column 2 have only 2 valence electrons. These metal families are most likely to give away their electron(s) to become positive cations. In other words, most metals become cations when involved in ionic bonds, especially those in Family 1 and Family 2. Some Metal Examples Gold Sodium Zinc Mercury Ionic Bonds and Anions What columns on the periodic table have 5, 6, or 7 valence electrons?_________ What would be easier (require less energy)? To give away 5, 6 or 7 electrons or bring in 1, 2, or 3 electrons to gain that octet? So: Nonmetals are found on the upper, right corner of the periodic table. Atoms in these families, such as families 16 and 17, have 6 and 7 electrons, resp. and are most likely going to gain electrons when involved in an ionic bond. In other words, the nonmetals become the anions when involved in an ionic bond. How do you know what kind of bond will form? Once you get into chemistry, you will be given some rules used to determine this with care. Since you are in Biology class for now, we are going to use a general-rule-of-thumb. It is the following: If the atoms joining, are on the right hand side of the stair step (nonmetals), you can assume the bond(s) will be covalent. If the atoms joining, are from opposite sides of the table (a metal with a nonmetal), you can assume the bond will be ionic. Examples: NaCl is ….. ionic H2O is ….. covalent CO2 is ….. Your Turn: CuF is _________ SO3 is _________ NO2 is _________ covalent Venn Diagram: Identify TWO similarities and TWO differences with IONIC and COVALENT bonds.