Structures and Bonding - Welcome to St. Aidan's Academy
28/02/20 EdExcel Unit C2 Discovering Chemistry N Smith St. Aidans 28/02/20 Topic 1 Atomic Structure and the Periodic Table 28/02/20 Periodic Table Introduction How would you arrange these elements into groups? 28/02/20 Development of the Periodic Table 1817: Johann Dobereiner developed the law of triads he put elements together in groups of 3 according to their properties. 1864: John Newlands arranged the known elements in order of atomic mass and found out that every 8th element had similar
properties: Li Be B C N O F Na Mg Al 1869: Dimitri Mendeleev arranged the known elements in order of mass but he also left in gaps and was able to predict the properties of unknown elements: Li Be B C N
O F Na Mg Al 1913: Henry Moseley proposed the use of atomic number rather than atomic mass. 28/02/20 The structure of the atom I did some experiments in 1808 that proved this and called these particles ATOMS. Most of an atom is empty space and the nucleus is actually very small so this diagram is wrong: Dalton NEUTRON neutral, same mass as proton PROTON positive, same mass
as neutron ELECTRON negative, mass nearly nothing 28/02/20 Mass and atomic number Particle Relative Mass Relative Charge Proton 1 +1 Neutron 1 0
Electron Very small -1 MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously) Atomic mass in more detail 28/02/20 RELATIVE ATOMIC MASS, Ar (Mass number) = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously) this number is always the same for 28/02/20 Mass and atomic number How many protons, neutrons and electrons?
Electron structure 28/02/20 Consider an atom of Potassium: Nucleus Potassium has 19 electrons. These electrons occupy specific energy levels shell s The inner shell has __ electrons The next shell has __ electrons The next shell has __ electrons The next shell has the remaining __ electron Electron structure = 2,8,8,1 Electron structure 28/02/20 Draw the electronic structure of the following atoms:
Nucleus Electron structure Nucleu s Electron structure Nucleu s Electron structure = 2,8,8,2 Periodic table 28/02/20 The periodic table arranges all the elements in groups according to their properties. Vertical columns are called GROUPS
Mendelee v Horizontal rows are called PERIODS 28/02/20 The Periodic Table Fact 1: Elements in the same group have the same number of electrons in the outer shell (this corresponds to their group number) H He Li Be B C N O
F Ne Na M g Al Si P S Cl Ar K Ca Br
Kr I Xe Fe Ni Cu Zn Ag Pt E.g. all group 1 metals have __ electron in their Au Hg These elements have __ electrons in their outer shells
These elements have __ electrons in their outer 28/02/20 The Periodic Table Fact 2: As you move down through the periods an extra electron shell is added: Li Be Na M g K Ca E.g. Lithium has 3 electronHin the configuration 2,1
He Fe 11 Ni Sodium has electrons in the configuration 2,8,1 Pt Cu Zn Ag Au Potassium has 19 electrons in the configuration __,__,__,__ Hg B C N
O F Ne Al Si P S Cl Ar Br Kr I Xe 28/02/20
The Periodic Table Fact 3: Most of the elements are metals: H These elements are metals He Li Be B C N O F Ne Na
M g Al Si P S Cl Ar K Ca Br Kr I Xe
Fe Ni Cu Zn Ag Pt Au This line divides metals from non-metals Hg These elements are non-metals 28/02/20 The Periodic Table Fact 4: (Most important) All of the elements in the same group have similar PROPERTIES. This is how I thought of the
periodic table in the first place. This is called H PERIODICITY. He Li Be B C N O F Ne Na M g Al
Si P S Cl Ar K Ca Br Kr I Xe Fe Ni Cu
Zn Ag Au Hg1 metals. E.g. consider thePtgroup They all: 1) Are soft 2) Can be easily cut with a knife Isotopes 28/02/20 28/02/20 An isotope is an atom with a different number of neutrons: Notice that the mass number is different. How many neutrons does each isotope have? Each isotope has 8 protons if it didnt then it just wouldnt be oxygen any more. 28/02/20 Strange atomic masses When you look at a periodic table
sometimes the atomic mass is not a whole number. Consider chlorine, for example: How can an atom have a decimal for its mass? This is because out of every four naturally occurring chlorine atoms, 3 have a mass of 35 and 1 has a mass of 37 so the average atomic mass is: (3 x 35 + 1 x 37) / 4 = 35.5 Q. Magnesium is often found as 24Mg or 26Mg. If 79% of magnesium is 24Mg what is the average atomic mass? (79 x 24 + 21 x 26) / 100 = 24.4 28/02/20 Topic 2 Ionic Compounds and Analysis Compounds Compounds are formed when two or more elements are chemically combined. Some examples: Glucose
28/02/20 Methane Sodium chloride (salt) How are these compounds formed? Lets consider two ways ionic and covalent bonding. 28/02/20 Introduction to Bonding C l Hi. My names Johnny Chlorine. Im in Group 7, so I have 7 electrons in my outer shell Id quite like to have a full outer shell. To do this I need to GAIN an electron. Who can help me?
C l Ionic Bonding Here comes a friend, Sophie Sodium C l Na Hey Johnny. Im in Group 1 so I have one electron in my outer shell. I dont like only having one electron there so Im quite happy to get rid of it. Do you want it? Okay + C l 28/02/20 Na
Now weve both got full outer shells and weve both gained a charge which attracts us together. Weve formed an IONIC bond. 28/02/20 Ions An ion is formed when an atom gains or loses electrons and becomes charged: + - The electron is negatively charged The proton is positively charged + If we take away the electron were left with just a positive charge: +
This is called an ion (in this case, a positive hydrogen ion, also called a cation). 28/02/20 Ionic bonding This is where a metal bonds with a non-metal (usually). Instead of sharing the electrons one of the atoms _____ one or more electrons to the other. For example, consider sodium and chlorine: Na Sodium has 1 electron on its outer shell and chlorine has 7, so if sodium gives its electron to chlorine they both have a ___ outer shell and are ______. + A _______ charged sodium ion (cation) Na
Cl Cl A _________ charged chloride ion (______) Group 1 _______ will always form ions with a charge of +1 when they react with group 7 elements. The group 7 element will always form a negative ion with charge -1. Words full, transfers, positively, negatively, metals, anion, stable Naming compounds 28/02/20 Rule 1 When two elements join and one is a halogen, oxygen or sulphur the name ends with ____ide e.g. Magnesium + oxygen oxide magnesium 1) Sodium + chlorine 6) KBr
2) Magnesium + fluorine 7) LiCl 3) Lithium + iodine 8) CaO 4) Chlorine + copper 9) MgS 5) Oxygen + iron 10)KF Naming compounds 28/02/20 Rule 2 When three or more elements combine and one of them is oxygen the ending is _____ate e.g. Copper + sulphur + oxygenCopper sulphate 1) Calcium + carbon + oxygen 6) AgNO3
2) Potassium + carbon + oxygen 7) H2SO4 3) Calcium + sulphur + oxygen 8) K2CO3 4) Magnesium + chlorine + oxygen 28/02/20 The Periodic Table Looking at their position in the Periodic Table and understanding their electron structure, we can predict the charge of different ions. What type of ion (and its charge) will elements from groups 2, 6 and 7 form? For example, group 1 elements all want to lose one electron so they will all form cations with a charge of +1
H He Li Be B C N O F Ne Na M g Al Si
P S Cl Ar K Ca Br Kr I Xe Fe Ni Cu Zn
Ag Pt Au Hg Some examples of ionic28/02/20 bonds Magnesium chloride: Mg + 2 + C l Mg C l Ca
- C l MgCl2 Calcium oxide: C l 2 + + O Ca 2- O CaO
Balancing ions 28/02/20 Some common ions: Sodium Na+ Chloride Cl- Potassium K+ Bromide Br- Magnesium Mg2+ Oxide O2- Ammonium NH4+ Sulphate SO42- Determine the formula of these compounds: Answers: 1) Sodium chloride
1) NaCl 2) Magnesium oxide 2) MgO 3) Magnesium chloride 3) MgCl2 4) Ammonium chloride 4) NH4Cl 5) Sodium sulphate 5) Na2SO4 6) Sodium oxide 28/02/20 Giant Ionic Structures When many positive and negative ions are joined they form a giant ionic lattice where each ion is held to the other by strong electrostatic forces of attraction
(ionic bonds). Cl- Na+ Cl- Na+ Cl- Na+ Na+ Cl- Na+ Cl- Na+ ClCl- Na+ Cl- Na+ Cl- Na+ Na+ Cl- Na+ Cl- Na+ Cl- If these ions are strongly held together what affect would this have on the substances: 1) Melting point? 2) Boiling point? 3) State (solid, liquid or gas) at room temperature? 28/02/20 Dissolving Ionic Structures When an ionic structure like sodium chloride is dissolved it enables the water to conduct electricity as charge is carried by the ions: Cl- Na+ ClNa+ Cl- Na+ Cl- Na+ ClNa+ Cl- Na+ Solubility rules 28/02/20 The following guidelines are useful in working out if a
substance will dissolve: All common sodium, potassium and ammonium salts are soluble All nitrates are soluble Common chlorides are soluble but not silver and lead Common sulfates are soluble but not those of lead, barium and calcium Common carbonates and hydroxides are insoluble except those of sodium, potassium and ammonium 28/02/20 Precipitation Reactions A precipitation reaction occurs when an insoluble solid is made by mixing two ionic solutions together. Method: 1) Mix the reactants together 2) Filter off the precipitate 3) Wash the residue 4) Dry the residue in an oven at 50OC 28/02/20 Precipitates
Some metal compounds form precipitates, i.e. an insoluble solid that is formed when sodium hydroxide is added to them. Consider calcium chloride: CaCl2 + 2NaOH Ca(OH)2 + 2NaCl What precipitates are formed with the following metal compounds when they react with sodium hydroxide? Metal compound Precipitate formed Calcium chloride Calcium hydroxide Aluminium chloride Magnesium chloride Ammonium chloride
Soluble or insoluble? Colour White Barium Sulfate Barium sulfate can be used as part of a barium meal to Xray patients. Why? 1) Barium sulfate is opaque to X rays so they will show up in an X ray 2) Its insoluble so it wont pass into the 28/02/20 Flame tests 28/02/20 Compounds containing lithium, sodium, potassium, calcium and barium ions can be recognised by burning the compound and observing the colours produced: Lithium
Sodium Red Yellow Potassiu m Lilac Calcium Barium Brick red Green 28/02/20 Testing for carbonate ions Limewater Limewater turns milky/cloudy Calcium carbonate + hydrochloric acid
calcium chloride + carbon dioxide + water 28/02/20 Testing for chloride and sulfate ions For each test state: 1) The colour of the precipitate 2) What compound it is Test 1: Chloride ions Add a few drops of dilute nitric acid to the chloride ion solution followed by a few drops of silver nitrate. Precipitate formed = silver chloride (white) Test 2: Sulphate ions Add a few drops of dilute hydrochloric acid to the sulphate ion solution followed by a few drops of barium chloride. Precipitate formed = barium sulphate (white again) Spectroscopy 28/02/20 Spectroscopy is kind of like a
flame test but using a spectroscope to see the results: Using this spectroscope I can see this: Each different element has a different signature when viewed through a spectroscope. This analysis enables us to detect the presence of small amounts of elements and this led to the discovery of new elements including rubidium and 28/02/20 Topic 3 Covalent Compounds and Separation Techniques Introduction to Bonding 28/02/20 Revision C l Hi. My names Johnny Chlorine. Im in Group 7, so I
have 7 electrons in my outer shell Id quite like to have a full outer shell. To do this I need to GAIN an electron. Who can help me? C l Covalent Bonding 28/02/20 Here comes another one of my friends, Harry Hydrogen C l Hey Johnny. Ive only got one electron but its really close to my nucleus so I dont want to lose it. Fancy sharing? C l
H Now were both really stable. Weve formed a covalent bond. H Covalent bonding 28/02/20 Consider an atom of hydrogen: Notice that hydrogen has just __ electron in its outer shell. A full (inner) shell would have __ electrons, so two hydrogen atoms get together and _____ their electrons: Now they both have a ____ outer shell and are more _____. The formula for this molecule is H 2. When two or more atoms bond by sharing electrons we call it ____________ BONDING. This type of bonding normally occurs between _______ atoms. It causes the atoms in a molecule to be held together very strongly but there are ____ forces between individual molecules. This is why covalently-bonded molecules have low melting and boiling points (i.e.
they are usually ____ or ______). Words gas, covalent, non-metal, 1, 2, liquid, share, full, weak, 28/02/20 Dot and Cross Diagrams Water, H2O: H H O 28/02/20 Dot and Cross Diagrams Oxygen, O2: O O 28/02/20 Dot and cross diagrams Water, H2O: Step 1: Draw the atoms with their outer shell:
H Step 2: Put the atoms together and check they all have a full outer shell: O H O H H Oxygen, O2: O O O O 28/02/20
Dot and cross diagrams Nitrogen, N2: Methane CH4: H N N H C H H Ammonia NH3: H Carbon dioxide, CO2: N H H O
C O 28/02/20 Other ways of drawing covalent bonds Consider ammonia (NH3): H N H H H N H H H N H
H Bonds formed between non-metals are usually covalent. Common examples are NH3, CO2, CH4, H2O etc. Properties of covalent28/02/20 Recall our model ofmolecules a simple covalent compound like hydrogen, H2: H H Hydrogen has a very low melting point and a very low boiling point. Why? 2) When a substance is 1) The intermolecular heated it is the forces are very weak so intermolecular forces that each one of these H2 are overcome, NOT the molecules doesnt really care about the others its covalent bond in each molecule, which is much
very easy to pull them stronger! apart. Also, the molecules do not carry a charge so covalent compounds usually do not conduct electricity. Giant Covalent structures 28/02/20 (lattices) Notice that giant covalent structures have very different properties to individual covalent molecules: 1. Diamond a giant covalent structure with a very ____ melting point due to ______ bonds between carbon atoms 2. Graphite carbon atoms arranged in a layered structure, with free _______ in between each layer O enabling carbon to conduct _________ (like metals) Si O 3. Silicon dioxide (sand) a giant covalent O O structure of silicon and oxygen atoms
O with strong _____ causing a high ______ Si Si O point and its a good insulator as it has no O O O O free electrons Words melting, high, electrons, bonds, strong,
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