1. 4.1 – Atomic Theory & Bonding

2. Matter …is anything with ______________ and _______________________.

3. Matter Mixture Pure Substance Element Compound (atom) (molecule)

4. Atoms & Molecules An atom is the smallest particle of an element that retains the properties of that element.  Ex: H  most* atoms consist of: proton(s) + neutron(s) + electron(s) 2 or more atoms can chemically combine in specific ways by sharing 1 or more pairs of electrons to form molecules. A molecule is the smallest particle of a (covalent) compound that retains the properties of that compound.  Ex: H 2 O

5. Chemical Change …involves breaking chemical bonds between atoms of pure substances, then rearranging the atoms and reforming bonds in new ways.

6. Atomic Theory atoms are made up of subatomic particles most of the atom’s volume consists of its electron cloud the atom’s mass comes from its protons and neutrons NameSymbolChargeLocationRelative Mass Protonp1836 Neutronn1836 Electrone1

7. Atomic Theory The nucleus is at the center of an atom, and consists of protons and neutrons. Electrons occupy energy levels / (electron) shells in the space surrounding the nucleus. in every atom of the same element: # of protons = # of electrons (by definition, an atom is _____) nuclear charge (charge on the nucleus) = # of protons atomic number = # of protons = # of electrons atomic mass = # of protons + # of neutrons

8. FYI for elements with atomic number ≤ 30... # of protons ≈ # of neutrons in heavier atoms… # of neutrons > # of protons  extra neutrons help to stabilize the nucleus but very heavy atoms have unstable nuclei, as the repulsion between protons is high

9. Organization of the Periodic Table The PT organizes all known elements.  elements are ordered by atomic number  atomic # increases… _______________ and ______________  metals are on the _______________  transition metals are ______________________  non-metals are on the ______________  metalloids form a “staircase” between ______________________  rows = periods  All elements in a period have their electrons in the same general area around their nucleus  columns = groups / families  elements in the same group… have similar chemical properties bond with other elements in similar ways

10. Organization of the Periodic Table GroupNameReactivity of Elements Group 1 Group 2 Group 17 Group 18

11. The Periodic Table Locate the following: Atomic Mass Atomic Number Period Group/Family Metals Non-metals Transition metals Metalloids Alkali metals Alkaline earth metals Halogens Noble gases INCREASING REACTIVITY

12. Periodic Table and Ion Formation Ion formation occurs when an atom gains or loses electrons. (Why not “…gains / loses protons”?)  ions are electrically charged particles  metals ________ electrons and become +ve ions  cations (remember: cats are positive!)  multivalent metals form ions in more than 1 way, depending on what they react with (the most likely ion to form is listed first in the box on the PT)  non-metals ________ electrons and become -ve ions  anions  Why do atoms tend to gain or lose electrons? http://www.brainpop.com/science/matterandchemistry/ions/

13. Bohr Diagrams Bohr diagrams show how many electrons appear in each electron shell around an atom (*not the positions / paths of e -s )  Each shell holds a maximum number of electrons  1 st e - shell holds ≤ ______ electrons  2 nd e - shell holds ≤ ______ electrons  3 rd e - shell holds ≤ ______ electrons  valence electrons occupy the outermost shell, and are the electrons involved in bonding  a stable octet is the arrangement of 8 e -s in the valence shell  think of the shells as being 3-D (like spheres), not 2-D (like circles) This is a Bohr diagram of which element?

14. Patterns of Electron Arrangement in Periods and Groups period # = # of shells in the atom the last digit of the group # = # of electrons in the valence shell (*except for the transition elements)

15. Forming Compounds When two atoms get close together, their valence electrons interact.  a chemical bond forms if the new arrangement of atoms & e -s is stable  stability is related to energy  lower energy states are more stable  lowest energy is achieved when valence e - configuration is the same as the closest noble gas on the PT  Metals may lose electrons and non-metals gain electrons (__________________________), OR  Atoms may share electrons (_______________________)

16. Ionic Bonds formed between ions of metals (cations, ___ve ions) and ions of non-metals (anions, ____ve ions) ≥ 1 electron transfers from each atom of the metal to each atom of the non-metal Ex. sodium and chlorine combine to form an ionic bond in the compound NaCl, which is called _________________

17. Practice with Ionic Bonds http://www.bbc.co.uk/schools/gcsebitesize/chemistry/classifyingmaterials/ionic_bondingrev5.shtml Ex. Using Bohr diagrams, show: 1.1 magnesium atom and 2 fluorine atoms 2.the transfer of electrons (using arrows) to form an ionic bond 3.the compound MgF 2, placing square brackets around each ion and showing the charge on each ion

18. Covalent Bonds formed between atoms of non-metals atoms overlap slightly, and ≥ 1 pair of electrons is shared  shared pair = “bonding pair”  unshared pair = “lone pair”

19. Practice with Covalent Compounds Ex. Draw Bohr diagrams of the following covalent compounds: a)H 2 Ob) NH 3

20. Lewis Diagrams Lewis diagrams ( / electron dot diagrams / Lewis structures) are useful for showing atoms’ bonding capabilities  only element symbol & valence electrons are shown  electron dots are placed singly around the element symbol (N, E, S, W) until the 5 th electron is reached, then they are paired

21. Comparing Bohr & Lewis Diagrams

22. Lewis Diagrams of Ions Lewis diagrams make drawing ions, and ionic bonds much easier than Bohr diagrams.  For cations, one electron dot is removed from the valence shell of the atom for each positive charge of the ion.  For anions, one electron dot is added to each valence shell of the atom for each negative charge of the ion.  Square brackets are placed around each ion to indicate transfer of electrons. BeCl Each Be atom has two electrons to “donate”, and each Cl atom “wants” one more electron BeCl BeCl Since Be 2+ wants to donate 2 electrons and each Cl – wants to accept only one, two Cl – ions are necessary beryllium chloride BeCl 2 2+ – –

23. Practice Drawing Lewis Diagrams of Ionic Compounds Ex. Draw Lewis diagrams of: a) scandium nitrideb) calcium chloride (c) McGraw Hill Ryerson 2007

24. Lewis Diagrams of Covalent Bonds Lewis diagrams of covalent bonds are also very easy.  Like Bohr diagrams, valence electrons are drawn to show sharing of electrons.  All atoms “wish” to have a full valence shell.  The shared pairs of electrons are usually drawn as a straight line.

25. Practice Drawing Lewis Diagrams of Covalent Compounds Ex. Draw Lewis diagrams of: a) NH 3 b) CH 4 (c) McGraw Hill Ryerson 2007

26. Lewis Diagrams of Diatomic Molecules O O O O O O Several non-metals join to form diatomic molecules Valence electrons are shared – two pairs! The 2 pairs are drawn as a double bond a diatomic molecule is a pair of atoms of the same element that are joined by covalent bonds the 2-atom molecule is more stable than the single atom seven diatomic molecules: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

27. Drawing Lewis Diagrams of Diatomic Molecules Ex. Draw Lewis diagrams of the following diatomic molecules: a)H 2 b) Cl 2 Ozone (O 3 ) is a triatomic molecule! http://www.elmhurst.edu/%7echm/vchembook/206bent.html http://www.elmhurst.edu/%7echm/vchembook/206bent.html http://www.bcscience.com/bc10/pgs/quiz_section4.1.htm