Atoms & Elements

Chapter Outline Development of Atomic Theories The composition of Atom Chemical properties of Atoms, the Periodicity and Periodic Table Isotopes

Experiencing Atoms Atoms: incredibly small, yet compose everything atoms are the pieces of Elements properties of the atoms determine the properties of the elements

Experiencing Atoms 91 elements found in nature Over 20 we have made in laboratories, and scientists are going to make more  Each element has its own, unique kind of atoms different structures different properties

Dalton’s Atomic Theory Elements are composed of atoms All atoms of an element are identical Atoms combine in simple, whole-number ratios to form molecules of compounds CO2 (O=C=O): 2 Oxygen atom + 1 Carbon atom H2O (H-O-H): 2 Hydrogen atom + 1 Oxygen atom In chemical reactions, atoms are not broken or changed into another type 2H2 + O2  2H2O John Dalton (1766-1844)

The Size of Atoms Atomic Mass Unit (amu): 1 amu = 1.66  10-24 g Hydrogen the smallest atom mass of H atom= 1.67 x 10-24g ~ 1 amu volume of H atom = 2.1 x 10-25cm3

About Electric Charge Rubbing dry paper towel and dry plastic piece causes plastic attracting small objects like styrofoam. Benjamin Franklin: Two Kinds of Charge: + and – Opposite Charges Attract: + attracted to – Like Charges Repel + repels + – repels – Neutral: no charge or equal amounts of opposite charges

Lightning: Neutralization of Charges accumulated between the clouds and the ground

1900s: The Atom is Divisible! Discovery of Electrons (J.J. Thomson et al.): The atom had pieces called electrons Electrons are much smaller than atoms and carry a “-” charge the mass of the electron is 1/1836th the mass of a hydrogen atom the charge on the electron is the fundamental unit of charge which we will call –1 charge units

What is Inside an atom. https://www. youtube. com/watch What is Inside an atom? https://www.youtube.com/watch?v=TKt3VuMMH_E (7-10 min) Ernest Rutherford’s experiment (1909): bombardment of a sheet of large atoms (as target) with small, high energy particles bullet = alpha particles, target atoms = gold foil a particles have a mass of 4 amu & charge of +2 c.u. gold has a mass of 197 amu & is very malleable

Rutherford’s Experiment Alpha Particles Striking Screen Radioactive Sample ~2% 0.01% >98% Lead Box Fluorescent Screen Gold Foil

Rutherford’s Results Thompson’s model of atom predicts there is no heavy mass or high charge within the atom, a particles should penetrate without obstruction > 98% of the a particles: went straight through ~2% of the a particles went through but were deflected by large angles ~0.01% of the a particles bounced off the gold foil: “...as if you fired a 15” canon shell at a piece of tissue paper and it came back and hit you.”

Rutherford’s Model of Atoms: Nuclear Atom . Atom mostly empty space because almost all the particles went straight through Atom contains a dense particle: small in volume compared to the atom but large in mass because of the few particles that bounced back “+” charge because of the large deflections of some of the particles

. Thompson’s Plum Pudding Atom was disproved by Experiment • Plum pudding model: all the a particles should go straight through a few of the a particles do not go through . Rutherford’s Nuclear Atom Model most a particles go straight through some a particles go through, but are deflected

Modern View of Atom Atoms = (Protons + Neutrons) + Electrons Nucleus: Protons + Neutrons, about 10-13 cm in diameter Electrons move outside the nucleus with an average distance of about 10-8 cm therefore the radius of the atom is about 100,000 times larger than the radius of the nucleus

Inside the Nucleus: Neutron and Protons Protons: “+” charge and a mass of 1 amu the number of proton equals the number of electrons in an atom (electrically neutral) Neutron: have no charge and a mass of 1 amu the masses of the proton and neutron are both approximately 1 amu

Elements each Element has a unique number of protons in its nucleus Atomic number: the number of Protons in the nucleus of an atom the elements are arranged on the Periodic Table in order of their atomic numbers each element has a unique name and symbol symbol either one or two letters one capital letter or one capital letter + one lower case

The Periodic Table of Elements

Get to know Elements: Name, Symbol, Atomic Number Element Name Symbol Atomic Number Lead Sb 79

Mendeleev: Periodicity order elements by atomic mass  repeating pattern of properties Periodic Law – When the elements are arranged in order of increasing relative mass, certain sets of properties recur periodically used pattern to predict properties of undiscovered elements A good documentary: Mendeleev (in the first 25 minutes, 20-25 min as my fav ) https://www.youtube.com/watch?v=yG0G_NkwOMc

Periodic Pattern: Compound with oxygen (ExOy) or with hydrogen (EHx) metal (m) or nonmetal (nm) oxide: acidic (a) or basic (b) H nm H2O a/b 1 H2 Compound w/ H Li m Li2O b 7 LiH Be m/nm BeO a/b 9 BeH2 nm B2O3 a 11 (BH3)n B nm CO2 a 12 CH4 C nm N2O5 a 14 NH3 N O nm OF2 19 HF F nm O2 16 H2O Na m Na2O b 23 NaH m MgO b 24 MgH2 Mg Al Si nm P4O10 a 31 PH3 P nm SO3 a 32 H2S S nm Cl2O7 a 35.5 HCl Cl m Al2O3 a/b 27 (AlH3) nm/m SiO2 a 28 SiH4

Periodicity = Metal = Metalloid = Nonmetal

Metals: Physical vs. Chemical Properties solids at room temperature, except Hg reflective surface shiny conduct heat, electricity Malleable (can be shaped) Tend to Lose electrons and form Cations in reactions. Na  Na+ + e - about 75% of the elements are metals lower left on the table

Nonmetals: Physical vs. Chemical Properties Elements found in all 3 states poor conductors of heat or electricity solids are brittle Tend to gain electrons in reactions to become anions: Cl + e -  Cl- upper right on the table except H He C N O F Ne P S Cl Ar Se Br Kr I Xe At Rn

Metalloids: between Metals and Nonmetals show some properties of metals and some of nonmetals also known as semiconductors VIIIA IVA VA VIA Properties of Silicon shiny conducts electricity does not conduct heat well brittle VIIA IIIA B IIB Si Ge As Sb Te Po

The Modern Periodic Table Elements with similar chemical and physical properties are in the same column Columns are called _________ or Families designated by a number and letter at top Rows are _______s each period shows the pattern of properties repeated in the next period Group period

The Modern Periodic Table Main Group = Representative Elements = ‘A’ Groups IA~VIIIA Transition Elements = ‘B’ groups: IB~VIIIB all metals Bottom rows = Inner Transition Elements = Rare Earth Elements metals really belong in Period 6 & 7

= Alkaline Earth Metals = Alkali Metals = Alkaline Earth Metals = Noble Gases = Halogens = Lanthanides = Actinides = Transition Metals add pictures of elements from text

= Transuranium element = Transition Metals = Rare Earth Metals = Transuranium element add pictures of elements from text U

Important Element - Hydrogen nonmetal colorless, diatomic gas H2 very low melting point & density reacts with Nonmetals to form molecular compounds HCl is acidic gas H2O is a liquid reacts with Metals to form hydrides metal hydrides react with water to form H2 Nickel-metal hydride (NiMH) used in rechargeable battery HX dissolves in water to form acids

Important Groups – IA, Alkali Metals Usually Hydrogen is included All metals: soft, low melting points Flame tests ® Li = red, Na = yellow, K = violet Chemical Property: Very reactive. React with water to form basic (alkaline) solutions and H2. releases a lot of heat Tend to form water soluble compounds, such as table salt and baking soda. colorless solutions lithium sodium potassium rubidium cesium

Important Groups – IIA, Alkali Earth Metals Physical properties: harder, higher melting, and denser than alkali metals flame tests ® Ca = red, Sr = red, Ba = yellow-green Chemical properties: reactive, but less than corresponding alkali metal form stable, insoluble oxides. oxides are basic = alkaline earth reactivity with water to form H2, ® Be = none; Mg = steam; Ca, Sr, Ba = cold water beryllium magnesium calcium strontium barium

Important Groups – VIIA, Halogens nonmetals F2 & Cl2 gases; Br2 liquid; I2 solid all diatomic (two atoms in one molecule) very reactive Cl2, Br2 react slowly with water Cl2 + H2O ® HCl + HOCl (chlorine water) react with metals to form ionic compounds HX all acids HF weak < HCl < HBr < HI fluorine chlorine bromine iodine

Important Groups – VIIIA, Noble Gases all gases at room temperature, very low melting and boiling points very unreactive, practically inert very hard to remove electron from or give an electron to

Ion: Charged Atom The number of protons determines the element! all sodium atoms have 11 protons in the nucleus In a chemical change, the number of protons in the nucleus of the atom doesn’t change! no transmutation during a chemical change!! during radioactive and nuclear changes, atoms do transmute Atoms in a compound are often electrically charged, these are called ions

Ions Atoms acquire a charge by gaining or losing electrons not protons!! Ion Charge = # protons – # electrons ions with a + charge are called cations more protons than electrons form by losing electrons ions with a – charge are called anions more electrons than protons form by gaining electrons

Atomic Structures of Cations Metals form cations More positive charge, the fewer electrons than the neutral atom Na atom = 11 p+ and 11 e-, Na+ ion = 11 p+ and 10 e- Ca atom = 20 p+ and 20 e-, Ca2+ ion = 20 p+ and 18 e- Cations are named the same as the metal sodium Na  Na+ + 1e- sodium ion calcium Ca  Ca2+ + 2e- calcium ion The charge on a cation can OFTEN be determined from the Group number on the Periodic Table Group 1A  +1, Group 2A  +2, (Al, Ga, In)  +3

Atomic Structures of Anions Nonmetals form anions For each negative charge the ion has 1 more electron than the neutral atom F = 9 e-, F- = 10 e- P = 15 e-, P3- = 18 e- Anions are named by changing the ending of the name to -ide fluorine F + 1e-  F- fluoride ion oxygen O + 2e-  O2- oxide ion The charge on an anion can be determined from the Group number on the Periodic Table Group 7A  -1, Group 6A  -2

Example: Find the number of protons and electrons in the Ca2+ ion The atomic number of Calcium is the number of ________ons. The number of electrons in an ATOM equals the number of _____ons. The “2+” charge means the ion has two _______ electrons Therefore the number of electron in Ca2+ ion = ____ __ ____ = ___ number of protons = _____ Number of electrons = _____

Example: Find the number of protons and electrons in the Ca2+ ion The atomic number of Calcium is the number of __protons. The number of electrons in an ATOM equals the number of _protons. The “2+” charge means the ion has two _fewer electrons Therefore the number of electron in Ca2+ ion = 20 – 2 = _18__ number of protons = _20_ Number of electrons = 18

Example: Find the number of protons and electrons in an I- ion The atomic number of iodine is the number of ________ons. The number of electrons in an ATOM equals the number of _____ons. The “-” charge means the ion has ONE _______ electrons Therefore the number of electron in I- ion = ____ __ ____ = ___ number of protons = _____ Number of electrons = _____

Example: Find the number of protons and electrons in an I- ion The atomic number of iodine is the number of _protons. The number of electrons in an ATOM equals the number of _protons. The “-” charge means the ion has ONE _more_ electrons Therefore the number of electron in I- ion = 53 + 1 = 54 number of protons = _53_ Number of electrons = _54_

Ion Charge & the Periodic Table The charge on an ion: an elements position on the Periodic Table Metals: always positive ions Na+ Ca2+ Al3+ Nonmetals are negative ions Cl- O2- N3- Main group metals: #charge = #group Magnesium ion = #Group = ______ Nonmetals, #ch Phosphide ion = #group – 8 = _____

Charge of ions by Group __ __ __ __ __ __ IA VIA IIA IIIA VA VIIA Li+ __ __ __ __ __ __ IA VIA IIA IIIA VA VIIA Li+ Be2+ N3- O2- F- Na+ Mg2+ Al3+ P3- S2- Cl- K+ Ca2+ Ga3+ As3- Se2- Br- Rb+ Sr2+ In3+ Te2- I- Cs+ Ba2+

Same Element, Different #Neutrons? Isotopes: The same element could have atoms with different masses 2 isotopes of chlorine found in nature: one has a mass of about 35 amu (Cl-35); another that weighs about 37 amu (Cl-37) Carbon-12 is much more abundant than Carbon-13. C-14 formed from nuclear reaction of N-14. The observed mass is a weighted average of the weights of all the naturally occurring atoms the atomic mass of chlorine is 35.45 amu

Isotopes all isotopes of an element: chemically identical undergo the exact same chemical reactions the same number of protons different masses due to different numbers of neutrons. Example: C-14 atom has eight neutrons; C-12 atom has six neutrons. identified by their mass numbers protons + neutrons

Isotopic Symbol Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17). The symbol for this isotope would be Cl 35 17 Atomic Symbol A = mass number Z = atomic number #neutrons = A - Z AX Z

Write the Isotopic symbol for Cr isotope w/ 27 neutrons Write down the given quantity, questions, and equations Given: Element, #neutron (#n) Find: #proton (#p) Find: #mass (A) Given: #p = Z, A = #p + #n #protons = _____ #mass = _____

Example: How many protons and neutrons in the chromium isotope

Practice - Complete the following table

Mass Number is Not the Same as Atomic Mass the atomic mass is an experimental number determined from all naturally occurring isotopes the mass number refers to the number of protons + neutrons in one isotope natural or man-made

From Atom to Ion Atom has equal number of positive charge (from protons) and negative charge (from electrons). Example: A calcium atom (symbol “Ca”) has 11 protons and 11 electrons A chlorine atom (Cl) has 17 protons and 17 electrons Metal loses electrons and becomes an ion with positive charge. A Ca atom loses TWO electrons, giving an ion with two positive charge: Ca2+ Nonmetal gains electrons and becomes an ion with negative charge. A Cl atom gains ONE electron, giving an ion with one negative charge: Cl-

Common Metal Cation Charge = + #Group Remember the following metal ions: Group IA = +1 Lithium ion ____ Potassium ion _____ Group IIA = +2 Magnesium ion ____ Barium ion _____ Silver ion:____ Zinc ion: ____ Aluminum: ____

Monatomic Nonmetal Anion (An-) The charge = #Group – 8 Name of the anion: change ending on the element name to –ide Group VA = -3 Group VIA = -2 Group VIIA = -1 N3- ____________ Oxide F- _______________ _______ Phosphide S2- __________ Chloride

Simple and Weighted Averages

Atomic Mass is the Weighted average of Mass Number Natural abundance of isotope: The percentage of #atoms for an isotope among all the naturally existing isotopes. Gallium: Ga-69 (mass number 68.926 amu, abundance 60.11%); Ga-71 (mass number 70.925, abundance 39.89%). Atomic mass of Gallium = 68.926 amu x 0.6011 + 70.925 x 39.89 = 69.72 amu

The Periodic Table

Chemistry Connection: Heavy Water