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September 22 Bellwork What are the three subatomic particles and their charges? What is an Atom? The smallest particle of matter that still has all of the properties and characteristics of that type of matter. A copper atom is the smallest particle of copper that still has all properties of copper. Brownian motion – the perpetual movement of particles (jiggling atoms) named after Robert Brown (Scottish Botanist) What Do Atoms Look Like? An atom is mostly empty space and contains what we call subatomic particles. They are electrons, protons and neutrons. Subatomic Particles Protons with a positive charge found in the nucleus of an atom Neutrons with a neutral charge also found in the nucleus of an atom Electrons with a negative charge found outside of the nucleus in the electron cloud The Periodic Table The elements are arranged according to characteristics in a grid-like structure, both how they look as well as the way they act Each box represents an element and each box contains the Atomic number (number of protons/electrons) Atomic mass number Chemical symbol Atomic Number The smaller number with no decimals Represents the number of protons and electrons in a neutral atom Periodic trend: increases from top to bottom and from left to right Example: If the atomic number is 2, then the atom has 2 electrons and 2 protons. Example 2: K has _19_ protons and _19_ electrons when neutral Atomic Mass Number The larger number with a decimal Measured in amu (atomic mass units) Represents the number of protons and neutrons in an atom Atomic Mass # = protons + neutrons Therefore… To find the number of neutrons: Neutrons = mass number – atomic number Example Carbon has a mass number of 12.011 and an atomic number of 6. How many protons does it have? Chemical Symbol Single letters or first letter capitalized If there are 3 letters, it is a man-made element that may get renamed Gold – Au (aurum) Iron – Fe (ferrum) Any element with an atomic number greater than 92 is manmade Isotopes Atoms of the same element with the same number of protons but different number of neutrons The mass number is an estimate of all of the possible isotopes of each element Isotopes are the reason that there is usually a decimal point in the atomic mass number Example of an Isotope C-12 has 6 neutrons, C-14 has 8 neutrons C-12 is more often found in nature, so the atomic mass of C is 12.011 which is closer to 12 than 14 How the Periodic Table is Set up Metals, Nonmetals, Metalloids Families (rows) and Periods (columns) Metals Located to the left of the zigzag (except hydrogen and metalloids) Properties: Luster (shine) Can be stretched and shaped Good conductors of heat/electricity Nonmetals Located to the right of the zigzag Properties: Dull Poor conductors of heat/electricity Metalloids/Semimetals/Semi-conductors Along the zigzag: B, Si, Ge, As, Te, Po Properties: Some are shiny but some are dull Not as good of conductors as metals but better than nonmetals Periods (Rows) and Families (Columns) Rows/Periods Horizontal Elements in the same period don’t have the same properties 7 on the periodic table Periods (Rows) and Families (Columns) Columns/Families Also called groups Vertical Elements in the same group/family have common properties 18 on the periodic table Li, Na, K all have a similar chemical reaction with water (H2O) They all create an explosion that releases hydrogen gas (H2) Therefore, they are stored with oil, not water. Valence Electrons The number of electrons in an atom’s outermost energy level Elements in the same group/family have the same number of valence electrons Atoms want to achieve a filled outermost energy level we call this an “octet” if the energy level contains 8 valence electrons Each Family of Elements Has its Own Name Alkali Metals Alkaline Earth Metals Transition Metals Halogens Noble Gases Alkali Metals Group 1 elements (except H) Have 1 valence electron Are the most active metals Tend to react with group 7 elements (halogens) Alkaline Earth Metals Group 2 elements Have 2 valence electrons Less reactive than alkali metals but still reactive Tend to react with group 6 Transition Metals Groups 3-12 on periodic table Metals, but different from alkali or alkaline earth metals Most have 1 or 2 valence e-s Include mercury (Hg) – the only liquid metal at room temperature Halogens Group 7 elements Some are gas, Br is liquid, and some are solid Have 7 valence e-s Tend to react with group 1 elements (alkali metals) Noble Gases Group 8 elements Helium has 2 valence e-s Ne, Ar, Kr, Xe, Rn, all have 8 valence e-s Are not reactive since they already achieved an octet Make up less than 1% of earth’s atmosphere Oxygen (21%), nitrogen (78%) contribute to most of the atmosphere Rare-Earth Elements Includes elements at bottom of periodic table (periods 6&7) First row = lanthanoid series (tend to be metals) Second row = actinoid series (most are man-made and radioactive) Names and Symbols of Commonly Used Elements Aluminum (Al) Boron (B) Calcium (Ca) Carbon ( C ) Chlorine (Cl) Copper (Cu) Helium (He) Hydrogen (H) Iron (Fe) Nitrogen (N) Oxygen (O) Sodium (Na) Gold (Au) We Can Use the Periodic Table to Draw Bohr Models A.k.a “planetary models” Protons, neutrons and electrons are represented in the Bohr Model We know that protons and neutrons are located in the nucleus at the center The electrons are located in the electron cloud in energy levels Energy Levels 1st level holds a max of 2 e 2nd level holds a max of 8 e 3rd level also holds 18 e- Lewis (Dot) Diagrams Electron dot diagrams are structures that show the valence electrons as dots Valence electrons are the electrons in the outermost shell and can be determined by looking at the group number on the periodic table Groups 1A – 8A (SKIP TRANS. METALS) If an element is in group 1A it has 1 V.E. If an element is in group 5A is has 5 V.E. Drawing Lewis Diagrams To draw the diagram: Write the symbol down Place dots around the symbol, one on each side and then begin to pair them Ions and Isotopes Isotopes: atoms of the same element with the same #p+ but different # of neutrons Mass Number: whole number; is only for one isotope of an atom Atomic mass: has decimal places because it is an average of the masses of all of the isotopes Ions An atom or molecule that has a charge. Loss of electrons Positive charge (cation) Gain of electrons Negative charge (anion) What is different between the 3 isotopes of hydrogen? Isotopes Isotopes= atoms of the same element that have the same atomic number but different atomic masses due to a different number of neutrons. Protons and neutrons have a relative mass of 1, and electrons are 1/1840, so electrons don’t really count when determining the mass. •Since most of the mass of the element is from protons and neutrons, changing the number of neutrons changes the mass of the atom. •To determine the atomic mass, scientists take an average mass of al isotopes of that atom. This gives us decimal places. Example of an Isotope Carbon-12 has a mass number of 12 •How many protons does it have? Why? •How many electrons does it have? Why? •How many neutrons does it have? Why? Example 2 Carbon-14 has a mass number of 14 •How many protons does it have? Why? •How many electrons does it have? Why? •How many neutrons does it have? Why? When scientists take the average of these masses to determine the atomic mass, they also consider which is more abundant (common) in nature. C-12 is more often found in nature so the atomic mass of C is 12.011, which is closer to 12 than 14. What happens if we don’t have the same number of protons and electrons? Then we no longer have a neutral atom! –Neutral atoms have NO charge –They have the same number of positive particles as negative particles. (They cancel each other out). Neutral Atom Example: –Oxygen has an atomic number of 8. –An atom of oxygen has 8p+ and 8e –So +8 + - 8 = 0 Ions In order for an atom to not be neutral, the number of electrons changes but the number of protons and neutrons stays the same Ion – atom with either a positive or negative charge (a charged particle) Neutral vs ion atom -2 O Protons = 8 Protons = 8 Neutrons = 8 Neutrons = 8 Electrons = 8 Electrons = 10 Formula: electrons = protons – charge e = 8 – (-2) Write the ion as either O2- or O-2 Boron ion Protons = Electrons = Neutrons = +3 B Formula: protons – charge = electrons If an atom has 7 protons and 10 electrons, what is its charge? •Negative ions are called ANIONS •Positive ions are called CATIONS Formula 1: Electrons = protons –charge Formula 2: Charge = protons – electrons Atomic Mass Units (amu) Today it is possible to determine the mass of an element using a mass spectrometer. However, numbers are small and impractical to work with. (i.e. Mass of F= 3.155 x 10 -23 g) It is easier to use relative masses of atoms using a reference isotope as a standard. Atomic Mass Units The reference isotope= Carbon 12. This isotope is assigned a mass of exactly 12 amu. Atomic mass units= 1/12 of the mass of a Carbon-12 atom. Atomic Mass In nature, most elements occur as a mixture of two or more isotopes. Atomic mass= the weighted average mass of the atoms in a naturally occurring samples of the element. Takes into account the relative abundance Atomic Mass To determine atomic mass, you must know the number of isotopes, the mass of each isotope and the percent abundance of each isotope. Atomic mass = multiply the mass of each isotopes by natural abundance and add the products. Atomic Mass of Carbon Example: Carbon has 2 isotopes: Carbon-12 which has a natural abundance of 98.89% (0.9889) and Carbon-13 which has a natural abundance of 1.11% (0.0111). Atomic Mass of carbon= Atomic Mass of Magnesium Magnesium has three naturally occurring isotopes. 78.70% of Magnesium atoms exist as Magnesium-24 (23.9850 g/mol), 10.03% exist as Magnesium-25 (24.9858 g/mol) and 11.17% exist as Magnesium-26 (25.9826 g/mol). What is the average atomic mass of Magnesium? Atomic Mass of Magnesium= Atomic Mass of Lithium What is the average atomic mass of Lithium if 7.42% exists as Li-6 (6.015 g/mol) and 92.58% exists as Li-7 (7.016 g/mol)? Atomic Mass of Lithium=