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UW-Milwaukee BIOSCI 150 - Atomic Number

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BIO SCI 150 1st Edition Lecture 4Atomic Number (Z)-Atoms of different elements differ by the number of protons in their nucleus, the number of protons existent is the atomic number.-On the periodic table, it is usually listed above the element.-Ex. Carbon’s (C) atomic number is 6Mass Number (A)-The number of Protons and neutrons in the nucleus of an atom.-This is generally found below the atom on the periodic table, it is never a whole number.-Ex. Carbon (C) has the atomic mass of 12.011Neutron Number (N)-The number of neutrons in the nucleus of an atomA=Z+N N=A-ZIsotopes-An isotope of an element is an atom that contains a specific number of neutrons.-Many elements have multiple isotopes-Ex. There are three isotopes of hydrogenIsotope Symbol-A common notation that represents the mass number, atomic number, and elemental symbol-The subscript (Z) is the atomic number-The superscript (A) is the mass number-Ex.Ions-Ions differ from atoms in that they have a charge, which is either greater than or less than the amount of protons.-Cations are positively charged-Anions are negatively charged-Dietary sodium and sodium found in the sea and in earth’s crust in the form of sodium ions.-A sodium ion has a net +1 charge: Na^+ (meaning it has one less electron than the number of protons)Atomic Mass-We can use mass number to compare the approximate relative masses of different isotopes-Ex. A carbon-12 is about ten times the mass of a hydrogen-1 atom-THE MASS NUMBER IS NOT THE ACTUAL MASS-The individual masses of the isotopes of an element can be determined by mass spectrometry- also used to determine relative amounts of the isotopes in a sample of an element.AMU Scale-The atomic mass unit (amu) scale was developed and based off of carbon-12 (meaning carbon-12 has a mass of 1 amu)-1amu =1/12 mass of 1 C-12 atomRelative Atomic Mass-The average mass of the individual isotopes of an element, taking into account the naturally occurring relative abundance of each-Carbon-12 is the most abundant isotope, so it makes sense that the relative atomic mass is 12.011 (very close)-Mass contribution from isotope = Isotope mass * relative abundance-Relative atomic mass = Mass contribution from first isotope + mass contribution from second isotopeThe Periodic Table-The first draft of the periodic table was developed between 1879 and 1871, and published by Dmitri Mendeleev.-Note that this was before the subatomic particles were discovered, so it was not based on atomic number.-The 63 known elements were arranged in order of increasing relative atomic mass, and elements with similar properties were grouped together.-He also grouped elements with similar properties into columns and rows so that the properties of the elements varied in a regular pattern (periodically).The Modern Periodic Table-Our current periodic table shows elements in order of increasing atomic number (#protons)-Elements in the same column have similar properties, and are called a group or family. Groups are designated in two ways:-A Roman numeral (I through VIII) and a letter (A or B)-An Arabic number (1-18)-A horizontal row of elements is a period. Elements in the same period have properties that tend to vary in a regular fashion. Periods are designated by an Arabic number (1-7).Metals, Nonmetals, and Metalloids-The periodic table has many classifications. Groups and periods are one classification. Another classification denotes metals, nonmetals, and metalloids.-A stair-step line starting at boron (B) separates metals (to the left of the line) from nonmetals (to the right of the line).-The metalloids exist along the line.-Metalloids are elements that have physical properties resembling a metal, but the chemical reactivity of a nonmetal.Classification of Elements Groups-IA Alkali metals (+1 charge)-IIA Alkaline Earth Metals (+2 charge)-VIIA Halogens (-1 charge)-VIIIA Noble Gases (no charge – everyone wants to be a noble gas)-Periods-Metals, Nonmetals, Metalloids-Main-group Elements, Transition Metals, and Inner-transition Metals.Main-Group Elements and Transition Metals-Main-group elements (also called representative elements) contain any element in the eight groups designated with the letter A. (In the Arabic numbering, groups 1, 2, and 13-18)-Transition metals contain any element in the 10 groups designated with the letter B. (In the Arabic numbering, groups 3-12)-Inner-transition metals contain the lanthanides and actinides listed separately at the bottom of the table.Elements that exist as Diatomic Molecules-Most elements, except for the noble gases, do not exist as single atoms.-The halogens, along with hydrogen, nitrogen, and oxygen, exist naturally as diatomic molecules when in their element form (not as compounds).-In total there are seven: Nitrogen, Oxygen, Hydrogen, Fluoride, Chlorine, Bromine, and IodineIons and the Periodic Table-The alkaline earth metals (Mg, Ca, …) all form ions with a 2+ charge.-Oxygen and sulfur react to form ions which have a 2- charge.-The halogens (F, Cl, Br, …) all form ions with a 1- charge.-The noble gases do not form ions. (least reactive)-Metals tend to loose electrons and become cations.Non-Metals tend to gain electrons and become anionsCommon Monatomic IonsIonic Compounds Contain Ions-Ions are very important and are components in many substances, our bodies and in our environment.-Ions are in ionic compounds, which will be discussed in the next


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UW-Milwaukee BIOSCI 150 - Atomic Number

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