Presentation on theme: "Unit 2 Chemistry and Radioactivity"— Presentation transcript:
1 Unit 2 Chemistry and Radioactivity Chapter 4: Atomic theory explains the formation of compounds
2 Words to Know: Chapter 4.1 - Atomic Theory and Bonding atomic number Bohr diagramcompound covalent bondingionic bonding ionsLewis diagram moleculevalence electrons
3 What is an Atom?smallest particle of an element that still has the properties of that elementAn atom = proton(s) + electron(s) + neutron(s) (PEN)Fun Fact:50 million atoms, lined up end-to-end = 1 cm
4 Pure Substances: Elements and Compounds are PURE SUBSTANCES Have their own unique properties that are always the sameAn ELEMENT is made up of one type of atomThe element, oxygen, is O.Atoms can join together to form MOLECULES.The oxygen molecules are O2COMPOUNDS are made up of several (2+)atomsHydrogen and oxygen are atoms/elementsH2O is a compound
5 Chemical Changes:occurs when the arrangement of atoms in compounds changeresults in a new compound
6 Structure of an Atom: The nucleus is at the centre of an atom composed of protons (positive charge) and neutrons (neutral charge)Electrons (negative charge) exist in the space surrounding the nucleus
7 area surrounding the nucleus Subatomic Particles:Atoms are made up of smaller particles known as sub-atomic particles.NameSymbolChargeLocationRelative MassProtonp1+nucleus1836NeutronnElectrone1–area surrounding the nucleus1
8 Numbers to Remember : # of protons = # of electrons in every atom AND ONLY IN ATOMS!!! (not ions)Nuclear charge = charge on the nucleus = # of protonsAtomic number = # of protons= # of electrons
9 The Periodic Table: The periodic table organizes the elements. elements are listed in order by atomic numbermetals are on the leftnon-metals are on the rightmetalloids form a “staircase” in the middle.Rows of elements (across) are called periodsall elements in a period have their electrons in the same valence shell (we’ll talk about this later!)
10 Families of the Periodic Table: Columns of elements are called groups, or familiesAll elements in a family have…similar propertiesbond with other elements in similar wayshave the same number of valence electronsFamily names:Group 1 = alkali metalsGroup 2 = alkaline earth metalsGroup 17 = the halogensGroup 18 = noble gases
11 Where are the following? INCREASING REACTIVITYWhere are the following?Atomic NumberPeriodGroup/FamilyMetalsNon-metalsTransition metalsMetalloidsAlkali metalsAlkaline earth metalsHalogensNoble gases
12 Periodic Table and Ion Formation: Atoms gain and lose electrons to form ions - electrically charged particles.Metals lose electrons and become positive ions (called cations)Some metals (multivalent) lose electrons in different waysie. Iron, Fe, loses either 2 (Fe2+) or 3 (Fe3+) electronsNon-metals gain electrons and become negative ions ( called anions)Atoms do this in an attempt to have the same number of valence electrons (electrons furthest from the nucleus) as the nearest noble gas.
13 Bohr Diagrams:Bohr diagrams show how many electrons appear in each electron shell around an atom.Each shell holds a maximum number of electrons (2, 8, 8, 18, 18)Electrons in the outermost shell are called valence electronsNote: Think of the shells as being 3D like spheres, not 2D like circles!
14 Bohr Diagrams What element is this? It has = 18 electrons, and therefore 18 protonsIt has 3 electron shells, so it is in period 3It has 8 electrons in the outer (valence) shell18 p22 nArgon!
15 Remember : Electrons appear in shells in a very predictable manner. There is a maximum of 2 electrons in the first shell, 8 in the 2nd shell, and 8 in the 3rd shell.The period # = # of shells in the atom.Except for the transition elements,the last digit of the group # = # of electrons in the valence shell
16 Note: The noble gas elements have full electron shells, and are very stable.
17 Forming Compounds:When two atoms get close together, their valence electrons interact.If the valence electrons can combine to form a low-energy bond, a compound is formed.Each atom in the compound attempts to have the stable number of valence electrons as the nearest noble gas.Metals may lose electrons and non-metals gain electrons, (ionic bond)ORAtoms may share electrons (covalent bond)
18 Bonding Types:Ionic bonds form when electrons are transferred from cations to anionsCations want to donate an electron (+) and anions want to accept more electrons (-)Covalent bonds form when electrons are shared between two non-metalsElectrons stay with their atom, but overlap with other shells
19 Electrons are transferred from the cations to the anion Ionic Bonds:Formed between cations (+ ions) and anions (- ions)Generally, this is a metal (+) and a non-metal (-)For example, lithium and oxygen form an ionic bond in the compound Li2O+LithiumOxygenElectrons are transferred from the cations to the anionLi+ O2- Li+Lithium oxide,Li2O
20 Covalent Bonds: Formed between two or more non-metals Electrons are shared between atoms+Hydrogen fluorideHydrogenFluorineElectrons are shared
21 Lewis Diagrams: Like simplified Bohr diagrams Only valence electrons are shownDots representing electrons are placed around the element symbols (on 4 sides, imagine a box around the symbol)Electron dots are placed singly, until the fifth electron is reached, then they are paired.Example: Nitrogen atom
22 Lewis Diagrams:Note: the Lewis diagrams are the same (except for the symbols) for elements in the same family because they have the same number of valence electrons
23 Lewis Diagrams for Ions: For positive ions: one electron dot is removed from the valence shell for each positive charge of the ion.For negative ions: one electron dot is added to each valence shell for each negative charge of the ion.Square brackets are placed around each ion to indicate a charge on the element
24 The ionic compound Beryllium chloride is formed –2+• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •BeClClBeClClBeClEach beryllium has two electrons to transfer away, and each chlorine wants one more electronSince Be2+ wants to donate 2 electrons and each Cl– wants to accept only one, two Cl– ions are necessaryThe ionic compound Beryllium chloride is formed
25 Lewis Diagrams For Covalent Bonds: Like Bohr diagrams, valence electrons are drawn to show sharing of electrons.All atoms “like” to have a full valence shellThe shared pairs of electrons are usually drawn as a straight line