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Chapter 4 “Atomic Structure” Subatomic particles of the atom Atoms are the building blocks of all Matter. Atoms are mostly empty space with a small dense core known as the Nucleus. Atoms are made up of 3 smaller particles (Subatomic Particles) : Protons, Neutrons, and Electrons Nucleus Makes up most of the mass of the atom. Made up of the following subatomic particles: Protons: positively charged Neutrons: neutral particles Has an overall + charge. Protons positively charged; Located inside nucleus; gives the atom its identity has the mass of 1atomic mass unit (amu) Same size as a neutron (1amu) Protons + Neutrons = the mass of the atom (atomic mass) Neutrons neutral charge; inside nucleus; has the mass of 1atomic mass unit (amu) Same size as a proton (1amu) Protons + Neutrons = the mass of the atom (atomic mass) Electrons negative charged has the mass of 1/1840 **note- electrons are extremely small compared to Protons & Neutrons Located in the electron cloud Electron Cloud- Area outside the nucleus where you are most likely able to find a nucleus. Subatomic Particles Particle Charge Mass Location Electron (e-) -1 1/1840 amu Electron cloud Proton (p+) +1 1 amu Nucleus Neutron (no) 0 1 amu Nucleus Amu= atomic mass unit= a unit used to measure the particles of an atom. = 1/12th the mass of a carbon atom Section 4.3 Distinguishing Among Atoms Atomic Number Elements are different because they contain different numbers of PROTONS. The number of Protons gives the atom its identity. The “atomic number” of an element is the number of protons in the nucleus. Atomic Number (# of protons) What makes an Atom Neutral? When an atom has the same number of protons as electrons. (+) = (-) if the atom is neutral then it has not lost or gained electrons. Atomic charge- an atom will have a charge when the protons and the electrons are not equal in number. Atoms will lose or gain electrons to become charged. Atoms that have a charge are called ions. Example: A sodium atom has 11 protons and 10 electrons. What is the charge? +11 protons (+) -10 electrons (-) --------------------Subtract +1 charge What is the Charge of these atoms? Which one is an Ion? 2 Protons (+) 6 Electons (-) ------------------------4 charge **** Ion **** 6 Protons (+) 6 Electons (-) -----------------------0 charge Isotopes Atoms of the same element can have different numbers of neutrons. Thus, different mass numbers. These are called isotopes. Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. Elements occur in nature as mixtures of isotopes. How to Name Isotopes Write the name then put the mass number after the name of the element: carbon-12 shorthand: C-12 carbon-14 shorthand: C-14 uranium-235 shorthand: U-235 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. The 3 Isotopes of Hydrogen Isotope Protons Electrons Neutrons Hydrogen–1 (protium) 1 1 0 Hydrogen-2 (deuterium) 1 1 1 1 1 2 Hydrogen-3 (tritium) Nucleus Mass number vs Atomic Mass Atomic Mass- Atomic mass is the average of all the naturally occurring isotopes of that element. the decimal you see on the periodic table An average of all the isotopes of that element. Mass number- the number of protons and neutrons in the nucleus of a specific isotope The mass of that specific isotope. Atomic Mass Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0 Nuclide Oxygen - 18 Neutrons = Mass # - p+ p+ n0 e- Mass # 8 10 8 18 Arsenic - 75 33 42 33 75 Phosphorus - 31 15 16 15 31 Complete Symbols Aka: Isotope Notation Contain the symbol of the element, the mass number and the atomic number. Mass Superscript → number Subscript → Atomic number X Symbols Find each of these: a) number of protons b) number of neutrons c) number of electrons d) Atomic number e) Mass Number 80 35 Br Symbols If an element has an atomic number of 34 and a mass number of 78, what is the: a) number of protons b) number of neutrons c) number of electrons d) complete symbol Symbols If an element has 91 protons and 140 neutrons what is the a) Atomic number b) Mass number c) number of electrons d) complete symbol Symbols If an element has 78 electrons and 117 neutrons what is the a) Atomic number b) Mass number c) number of protons d) complete symbol Complete Symbols of an ION If the symbol has a superscript on the right side, it has lost or gained electrons. Superscript → Mass number Atomic Subscript → number # of electrons lost or gained X • Negative number = # of electrons it has gained • Positive number = # of electrons it has lost Atomic Mass How heavy is an atom of oxygen? It depends, because there are different kinds of oxygen atoms. We are more concerned with the average atomic mass. This is based on the abundance (percentage) of each variety of that element in nature. We don’t use grams for this mass because the numbers would be too small. Measuring Atomic Mass Instead of grams, the unit we use is the Atomic Mass Unit (amu) It is defined as one-twelfth the mass of a carbon-12 atom. Carbon-12 chosen because of its isotope purity. Each isotope has its own atomic mass, thus we determine the average from percent abundance. To calculate the average: Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results. If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu) Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Isotope Symbol Carbon-12 12C Carbon-13 13C Carbon-14 14C Composition of the nucleus 6 protons 6 neutrons 6 protons 7 neutrons 6 protons 8 neutrons Carbon = 12.011 % in nature 98.89% 1.11% <0.01% Practice Problem: Element X has 2 Natural occurring isotopes. Isotope 10X has the mass of 10.012 and a relative abundance of 19.91% . The other istotope 11X has the mass of 11.009 and the abundance of 80.09%. Calculate the average atomic mass of this element. Mass X Abundance (changed to a decimal) 10X: 10.012amu X 0.1991 = 1.993 amu 11X: 11.009amu X 0.8009 = 8.817 amu ---------------------------------------------------Add-------------Average Atomic Mass = 10.810 amu The Periodic Table: A Preview A “periodic table” is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties The periodic table allows you to easily compare the properties of one element to another The Periodic Table: A Preview Each horizontal row (there are 7 of them) is called a period Each vertical column is called a group, or family Elements in a group have similar chemical and physical properties Identified with a number and either an “A” or “B” More presented in Chapter 6