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The periodic table organizes all known elements. Elements are listed in order by atomic number

The periodic table organizes all known elements. Elements are listed in order by atomic number Metals are on the left (the transition metals range from group 3 - group 12) Non-metals are on the right , Metalloids form a “staircase” in the middle.

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The periodic table organizes all known elements. Elements are listed in order by atomic number

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  1. The periodic table organizes all known elements. • Elements are listed in order by atomic number • Metals are on the left • (the transition metals range from group 3 - group 12) • Non-metals are on the right, • Metalloids form a “staircase” in the middle. • Rows of elements (across) are called periods. • All elements in a period have their electrons in the same general area around their nucleus

  2. Columns of elements are called groups, or families • All elements in a family have similar properties, and bond with other elements in similar ways • Group 1 = alkali metals • Group 2 = alkaline earth metals • Group 17 = the halogens • Group 18 = noble gases

  3. Bohr Models… • Niels Bohr explained the structure of the atom in his “Bohr models”. His model of the atom resembles a solar system. He came up with this model in 1913. Here is a typical Bohr model, what can you figure out from it

  4. Bohr models show the nucleus in the center with the # of Protons (p) and Neutrons (n) in it • Around the nucleus, it shows • the electrons in orbits or shells • Each orbit/shell can only hold a certain # of electrons and then it is full.

  5. How many e- can each orbit hold? • 1st orbit can hold 2 e- • 2nd orbit can hold 8 e- • 3rd orbit can hold 8 e- • 4th orbit can hold 18 e- • You don’t need to know any higher orbits – we won’t be covering higher elements. • You can depict any element in a Bohr model!

  6. Some Bohr models… Beryllium 4 p+ 5n 4e- Oxygen 8p+ 8n 8e- Aluminum

  7. So how do we draw a Bohr model of… say…Sodium? • Start with a nucleus, and put in how many protons and neutrons are in sodium (look at your periodic table) • Next place some orbits around it P: 11 N:12 P: 11 N:12

  8. Next figure out how many e- are in sodium (look at your periodic table). Place them in dots in the orbits Remember!! 2 max in 1st orbit 8 max in 2nd orbit 8 max in 3rd orbit 18 max in 4th orbit Sodium has 11 electrons !! they are the same as the protons P: 11 N:12

  9. The outermost electrons – the ones in the last shell/orbit are called valence electrons • Valence e- are important because when atoms react, it is the valence e- that do all the moving !! P: 11 N:12 * Think valence penguins

  10. How many Valence e- in these Bohr models?? 2 ve- 6 ve- 3 ve-

  11. Valence e- what do we know… • Which group on the periodic table, do you notice, always has all it’s valence electron shell full? • The Noble Gases. This is very significant… Why?? • Because every element wants to have a full outer shell of valence e- – because then it is completely stable and never has to react.Every element wants to be a noble gas

  12. Ion Formation • An ion forms when an atom gains or loses electrons. • Metals lose electrons and become positive ions (= cations) • Some metals (multivalent) lose electrons in different ways • ie. Iron, Fe, loses either 2 (Fe2+) or 3 (Fe3+) electrons • Non-metals gain electrons and become negative ions ( = 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. Cations (positive charge) are attracted to anions (negative charge) and a chemical bond is formed ~ A new compound! ~ ~

  13. Forming Compounds • Bonds between metals and non-metals are formed by ion formation (Ionic Bonding). • Bonds between 2 non-metals are formed when electrons are shared between atoms ~ No ions are formed! • Electrons stay with their atom, but overlap with other shells • This is called covalent bonding. Metals do not bond together! Metals can be combined by melting into alloys but there is no chemical bond formed.

  14. What about Bohr models of Molecules? • Eg. What is this compound? 1p+ 0n 8 p+ 8 n 1p+ 0n

  15. Can you answer these questions… • Can you draw the Bohr model of H2? • Why would 2 Hydrogens be happy to bond together? 1p+ 0n 1p+ 0n

  16. Forming Compounds with Bohr • 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 • Covalent bonds • Formed between two or more non-metals • Electrons are shared between atoms + Electrons are transferred from the cations to the anion Li+ O2- Li+ Lithium oxide, Li2O Oxygen Lithium + Hydrogen fluoride Electrons are shared Fluorine Hydrogen

  17. Lewis Dot Diagrams… • Bohr had one way of depicting the atom and it’s sub atomic particles (p+, n, and e-). But another man, Gilbert Lewis used a different model, and he only showed the valence e- in it. His model is called the Lewis dot diagram He put dots around the symbols so that we can see the valence electrons for the elements (we can easily see which e- are going to react)

  18. The red dots show you the valence electronsin each element’s atoms

  19. Lewis Dot Structures

  20. Lewis Dot Structures • Lewis dot structures are really simple – they are just the valence e- represented as dots around an element. 2 electrons can be shown as 2 dots or by 1 line. 2 electrons together is called a lone pair. Pd The # of valence e- is … 8 8 is the # we want – it’s stable – like a noble gas

  21. How to draw …

  22. Try some now… • Remember, up to 4 e-, you put separately on each side of the symbol, once you get to 5, you have to start pairing up. 1) Magnesium 2) Nitrogen 3) Flourine 4) Argon Bonding pair N Mg F Ar

  23. So what happens when atoms meet? • When 2 atoms move close together, their valence electrons interact, and they form a chemical bond between them if they are a good pair (more stable together than apart) • Having a full valence shell is what each element wants! So it will bind with other elements that make that happen!

  24. Lewis Diagrams of ions • Lewis diagrams make drawing ions, and ionic bonds much less work than Bohr diagrams. • 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 transfer of electrons – 2+ – • • • • • •• •• • • • •• •• • • • •• •• • • • • •• •• • • • • •• •• •• Be Cl Cl Be Cl Cl Be Cl Each beryllium has two electrons to transfer away, and each chlorine wants one more electron Since Be2+ wants to donate 2 electrons and each Cl– wants to accept only one, two Cl– ions are necessary Beryllium chloride

  25. 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

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