UNIT 1 THE SCIENTIFIC WORK

UNIT 5ELEMENTS AND COMPOUNDSJ. Fidalgo1

THE PERIODIC TABLE OF ELEMENTSAn element is a substance that cannot be separated into simpler substances by chemical methodsElements are the building blocks of nature, being composed of only one kind of identical particles called atoms, all with the same proton number.The periodic table is the most important tool a chemist possesses.It is a way of ordering the chemical elements in such a way that demonstrates the periodicity of the chemical and physical properties.

HISTORY OF THE PERIODIC TABLEAlthough elements such as gold (Au), silver (Ag), tin (Sn), copper (Cu), lead (Pb) and mercury (Hg) have been known since antiquity, the first scientific discovery of an element was the discovery of phosphorus (P) in 1649 by the German alchemist Hennig Brand.

HISTORYJohann W. Dbereiner noticed that the atomic mass of strontium (Sr) was halfway between the masses of calcium (Ca) and barium (Ba) and all three possessed similar chemical properties.He then began to group elements with similar chemical properties into sets of three or triads.

HISTORYJohn Newlands classified the known 56 elements into 11 groups based on similar physical properties. He noticed that many pairs of similar elements existed with atomic masses that differed by a multiple of eight, and hence he proposed the Law of Octaves based on an analogy with the musical scale.

HISTORYMendeleev made up cards, each card had an element symbol, its atomic mass and its properties. He arranged the cards in order of ascending atomic mass, grouping elements of similar properties together. When the pattern began to go wrong, he left a gap in his table claiming that those gaps were for elements that had not yet been discovered. He even changed the order around when similar elements didnt line up.

HISTORYBut Mendeleev's table needed one important modification before it became the modern periodic table: the use of the atomic number (number of protons) instead of the relative atomic mass to order the elements. It was first proposed by the British chemist Henry Moseley in 1913.The last major changes to the periodic table resulted from Glenn Seaborg's work in the middle of the 20th Century. He reconfigured the periodic table by placing two rows of ten elements, called transition metals or rare earths, below the main body of the table to make it more compact and manageable.

THE PERIODIC TABLE OF ELEMENTShttps://www.youtube.com/watch?v=0RRVV4Diomg

GROUPS AND PERIODS

METALS, NON METALS AND METALLOIDS

METALS-NON METALS-METALLOIDS-NOBLE GASES

NOBLE GASESThe six noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon(Xe) and radon (Rn). They are found in group 18 of the periodic table. The most striking thing about this family is their lack of reactivity. That is, they undergo chemical reaction with very few substances. These elements were considered to be absolutely inert gases until 1962, when the first compound of xenon and fluorine (xenon tetrafluoride, XeF4 ) was made. Nowadays more than 20 compounds containing noble gases, most of them with xenon, are known.All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others. Since they are so chemically stable, it has been concluded that a full outer shell makes an atom stable.

NOBLE GASES

Noble gases are all colourless and monoatomic (their particles are single atoms). But the six noble gases are not identical:The boiling points of the noble gases increase as we go down the group. This is because the attraction between molecules gets stronger as the molecules get larger.The density of the noble gases increases as we go down the group. This is because the mass of the atoms increases.METALS AND NON METALS

METALSPHYSICAL PROPERTIEShigh melting point, so theyre solid at room temperature (with the exception of mercury, Hg, a liquid).shiny (when they are pure and clean).good conductors of electricity and heatductile (they can be drawn out into thin wires)malleable(they can be easily hammered into very thin sheets).

CHEMICAL PROPERTIESMetals have few electrons in their outer shell, so they tend to lose electrons easily to enhance their stability, forming positive ions (M+).silver ion Ag+, magnesium ion Mg2+, aluminium ion Al3+They react with oxygen to form certain substances called oxides.Example:magnesium + oxygen magnesium oxide, MgOMetals react with non-metals to form substances called binary salts.Example: sodium + chlorine sodium chloride, NaClMetals react with acids, and hydrogen gas is given off.Example :zinc + hydrochloric acidzinc chloride + hydrogenNON METALSPHYSICAL PROPERTIESNon-metals can be gases at room temperature (hydrogen, oxygen, fluorine, chlorine and nitrogen), but others are liquids (bromine) or solids with low melting points (iodine, sulphur, phosphorous, carbon, etc). Nevertheless, carbon in the form of diamond has a very high melting point.brittle (they break without significant deformation)Neither malleable nor ductilePoor conductors of both heat and electricity (although carbon in the form of graphite is a good conductor of electricity)CHEMICAL PROPERTIESThey have their outer electronic shell incomplete, with a few empty spaces for electrons. Hence, in chemical reactions they tend to gain electrons to fill up their outer shell and enhance their stability.Non-metals react with oxygen to form substances called non-metal oxides. At room temperature these oxides are often gases.Example: sulphur + oxygen sulphur trioxide, SO3 Most non-metal oxides can be dissolved in water to form substance called oxoacids.Example:sulphur trioxide + water sulphuric acid, H2SO4

SEMI-METALSThe elements that border the stair stepped line in the periodic table are classified as semi- metals or metalloids.They have properties that are somewhat of across between metals and non-metals.They are economically important because of their unique electric properties (they conduct electricity only in certain conditions),which make them valuable in the electronic and computer industry .Silicon (Si) is the most well-known semi-metal. It behaves like a metal in some ways, but like a non-metal in others. For example, it is shiny like a metal, but brittle like a non-metal.

CHEMICAL BONDING: Why compounds are formed?

Only the noble gas atoms have full outer shells.The atoms of all other elements have incomplete outer shells. That is why they react. By reacting with each other, atoms can obtain full outer shells and so become stable.When atoms react in order to form full shells of electrons, they lose or gain share. These electrons are called valence electrons.The valence of an element tells you the number of electrons its atoms lose or gain or share.

CHEMICAL BONDINGA chemical bond is an attraction between atoms brought about by a sharing of electrons between to atoms or a complete transfer of electrons.There are three types of chemical bonds: Ionic,CovalentandMetallic.In addition chemists often recognize another type of bond called ahydrogen bond.

CHEMICAL BONDING: a chemical party

IONIC BONDINGMetal atoms need to lose electrons, and non-metal atoms need to gain electrons, so metals combine with non-metals to form an ionic bond.

Losing electronsGaining electrons

IONIC BONDINGWhen a sodium atom and a chlorine atom react together, the sodium atom loses its electron to the chlorine atom, and two ions are formed.As you know, opposite charges attract. Therefore, the Na+ ions and CI- ions are strongly attracted to each other.This attraction sticks the ions together, and it is called an ionic bond, or sometimes an electrovalent bond.

IONIC BONDINGThe pattern grows until a giant structure of ions is formed. Millions of ions bond together to form crystals. It contains equal numbers of sodium and chloride ions.This giant structure is the compound sodium chloride or salt.Because sodium chloride is made of ions, it is called an ionic compound. It contains one Na+ ion for each Cl- ion, so its formula is NaCl. The charges in the structure add up to zero. The compound therefore has no overall charge.

IONIC BONDINGIonic bonding is the complete transfer of valence electron(s) between atoms.It is a type of chemical bond that generates two oppositely charged ions.In ionic bonds, the metal loses electronsto become a positively charged ion (cation), whereas the non-metal accepts those electronsto become a negatively charged ion (anion).Ionic bonds require an electron donor, metal, and an electron acceptor, non-metal.

IONIC BONDING: PROPERTIESScientists found that the ions form giant structures (lattices). And it explains the properties observedThey are made of crystals (which can be split along certain angles). They have high melting pointsThey are often soluble in waterThey conduct electricity when molten or dissolved in water, but not when solid.

IONIC BONDING

NAMING IONIC COMPOUNDSThe metals form cations (positive ions), which have the same name as the atoms. The non-metals form anions (negative ions) and their names end in ide. To name an ionic compound, you just put the names of the ions together, with the positive one first.The formulae of ionic compounds can be worked out by the following steps:Write down the name of the ionic compound.Write down the symbol for its ions.The compound must have no overall charge, so balance the ions, until the positive and negative charges add up to zero.Write down the formula without the charges.

Ions in compoundsName of compoundFormulaeK+ and F-Potassium fluorideKFCa2+ and Br-Calcium bromideCaBr2K+ and H-Potassium hydrideK HLi+ and O2-Lithium oxideLi2ONAMING IONIC COMPOUNDSTransition metal ions: Some transition metals form only one type of ion (Ag+; Zn2+), but most of them can form more than one type.

IonsNameExample of compoundCu+copper (I) ionCopper (I) oxide, Cu2OCu2+copper (II) ionCopper (II) oxide, Cu OFe2+iron (II) ionIron (II) chloride, FeCl2Fe3+iron (III) ionIron (III) chloride, FeCl3

(The roman numbers, I, II or III in a name show that the ion has a charge of 1+, 2+ or 3+.)NAMING IONIC COMPOUNDSCOMPOUND IONSSo far, all the ions have been formed from single atoms. But ions can also be formed from groups of joined atoms. These are called compound ions or polyatomic ions.

TYPES OF CHEMICAL BONDING