Presentation on theme: "States of Matter The Particle Theory of Matter: 1. Matter is made up of tiny particles (Atoms & Molecules) 2. Particles of Matter are in constant motion."— Presentation transcript:
States of Matter The Particle Theory of Matter: 1. Matter is made up of tiny particles (Atoms & Molecules) 2. Particles of Matter are in constant motion. 3. Particles of Matter are held together by very strong electric forces 4. There are empty spaces between the particles of matter that are very large compared to the particles themselves. 5. Each substance has unique particles that are different from the particles of other substances 6. Temperature affects the speed of the particles. The higher the temperature, the faster the speed of the particles.
Chemical Equations A chemical equation summarizes what happens to substances during a chemical reaction. For example, the combustion of methane (in oxygen) is depicted as: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)
Periodic Table of Elements The periodic table of elements arranges elements into periods (horizontal rows) and groups (vertical columns) according to their atomic numbers. The atomic number is the number of protons in an atomic nucleus. The entire table can be separated by metals (green), metalloids (pink) and non-metals (blue).
Predicting Chemical Reactivity Electron shell diagrams are useful because they show the numbers of electrons in the shells of atoms. Knowing the number of outer shell electrons helps you predict the formation of compounds, and write their chemical formulas. A chemical bond forms between two atoms when electrons in the outer shell of each atom form a stable arrangement together. The outer shell is called the valence shell. The electrons that occupy it are called valance electrons.
Positively Charged: Cations Any atom or group of atoms that carries an electrical charge is called an ion. When a neutral atom gives up an electron, the positively charged ion that results is called a cation. Alkali metals form cations easily and are chemically very reactive. When elements gain one electron they become negatively charged particles called anions.
Electron Dot Diagrams (Lewis Structures) In any group, all the elements have atoms with the same number of valence electrons. You can use a simple model called an electron dot diagram or Lewis diagram, to represent an atom and its valence electrons.
Forming Compounds Atoms may share electrons between other atoms creating bonds. Substances that are composed of cations and anions are called ionic compounds. The attraction between the oppositely charged ions is called an ionic bond. Nearly all ionic compounds involve bonds between metal cations and non-metal anions. -Ionic compounds tend to have relatively high melting points because a large of amount of energy is needed to break the strong forces of attraction in ionic bonds. -Ionic compounds conduct electricity when they are molten or when they are dissolved in water. This is because the ions are able to move freely. -Ionic compounds in the solid state are not electrical conductors since the ions are not able to move
Forming Compounds Atoms that share a pair of electrons are joined by a covalent bond. A neutral particle that is composed of atoms joined together by covalent bonds is called a molecule. Substances that are composed of molecules are called molecular compounds. Molecular compounds are formed when atoms of non-metals are joined by covalent bonds. Although the bonds between atoms within the molecule are strong, the force of attraction between the molecules is weak. -Molecular compounds have relatively low melting points because little energy is needed to break the forces of attraction between molecules. -Molecular compounds tend not to conduct electricity when they are in the solid or liquid state, or when they are dissolved in water, because they do non contain ions.
Chemical Names and Formulas The system for naming an ionic compound is different from that for naming a covalent compound, so before a compound can be named, it must be classified as ionic or covalent. Classifying a compound is not an easy task, but for the purposes of naming them, we employ a simple test: Is there a metal or a polyatomic ion present? A polyatomic ion consist of two or more different non-metal atoms, which are joined by covalent bonds. If the answer is yes, use the system for naming ionic compounds. If the answer is no, use the system for naming covalent compounds.
Naming Ionic Compounds (continued) If a Roman numeral is required, the charge on the metal ion must be determined from the charge on the negative ion. Helpful Rules to Remember FormulaReasoningName FeCl 2 Cl has a 1- charge, and there are 2 of them for a total of 2-, so the Fe must be 2+ iron (II) chloride Fe 2 O 3 O has a 2- charge, and there are 3 of them for a total of 6-, so the Fe must have a total charge of 6+ split equally between the two iron atoms, so each must have a 3+ charge iron (III) oxide PbS 2 S has a 2- charge, and there are 2 of them for a total of 4-, so the Pb must be 4+ lead (IV) sulfide Cu 3 N N has a 3- charge, so the Cu must have a total charge of 3+ split equally between the 3 copper atoms, so each must have a 1+ charge copper (I) nitride Examples A metal ion is always positive. The Roman numeral indicates the charge, not the subscript. The positive and negative charges must cancel (total charge must = 0). Nonmetals are always negative & can never form more than one monatomic ion.
Naming Ionic Compounds (continued) II. Polyatomic ions each have specific names which must be memorized so they can be recognized on sight. (At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.) FormulaName C 2 H 3 O 2 1- acetate CO 3 2- carbonate HCO 3 1- bicarbonate NH 4 1+ ammonium A few of the more common polyatomic ions FormulaName NO 3 1- nitrate OH 1- hydroxide PO 4 3- phosphate SO 4 2- sulfate
Naming Ionic Compounds: Examples Na 2 SO 4 sodium sulfate Fe(NO 3 ) 2 iron (II) nitrate AlCl 3 aluminum chloride PbI 4 lead (IV) iodide (NH 4 ) 3 PO 4 ammonium phosphate Mg 3 N 2 magnesium nitride C 2 H 3 O 2 1- acetate CO 3 2- carbonate HCO 3 1- bicarbonate NH 4 1+ ammonium NO 3 1- nitrate OH 1- hydroxide PO 4 3- phosphate SO 4 2- sulfate * Groups I & II, Al, Zn, Cd, and Ag need no Roman numeral. AgC 2 H 3 O 2 silver acetate
Naming Covalent Compounds Covalent compounds are named by adding prefixes to the element names. The compounds named in this way are binary covalent compounds. ‘Binary’ means that only two atom are present. ‘Covalent’ (in this context) means both elements are nonmetals. A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.) A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘ide’.
Naming Covalent Compounds Prefixes SubscriptPrefix 1mono- 2di- 3tri- 4tetra- 5penta- SubscriptPrefix 6hexa- 7hepta- 8octa- 9nona- 10deca- Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.
Naming Binary Covalent Compounds: Examples N 2 S 4 dinitrogen tetrasulfide NI 3 nitrogen triiodide XeF 6 xenon hexafluoride CCl 4 carbon tetrachloride P 2 O 5 diphosphorus pentoxide SO 3 sulfur trioxide 1mono 2di 3tri 4tetra 5penta 6hexa 7heptaa 8octa 9nona 10deca * Second element in ‘ide’ from * Drop –a & -o before ‘oxide’
Naming Compounds: Practice SiF 4 silicon tetrafluoride Na 2 CO 3 sodium carbonate N 2 O dinitrogen monoxide K 2 O potassium oxide Cu 3 PO 4 copper (I) phosphate CoI 3 cobalt (III) iodide AnalysisIf “Yes” * Is the cation a metal? (If so, does it need a Roman numeral? The compound is ionic: name each ion present (DO NOT USE PREFIXES) * Is there a polyatomic ion present? * Are both elements nonmetals? The compound is covalent: use prefixes (NO CHARGES EXIST) PI 3 phosphorus triiodide two nonmetals covalent use prefixes metal present ionic no prefixes Na group I no Roman numeral two nonmetals covalent use prefixes metal present ionic no prefixes K group I no Roman numeral metal present ionic no prefixes Cu not group I, II, etc. add Roman numeral (PO 4 is 3-, each Cu must be 1+) metal present ionic no prefixes Co not group I, II, etc. add Roman numeral (I is 1-, total is 3-, Co must be 3+) two nonmetals covalent use prefixes NH 4 Cl ammonium chloride NH 4 polyatomic ion present ionic no prefixes
Writing Chemical Formulas: A Review I. Ionic Compounds II. Covalent Compounds
Classifying Compounds Classifying a compound using its name is not as difficult as using its formula. The names of covalent compounds will be easily recognized by the presence of the prefixes (mono-, di-, tri-, etc.). If no prefixes are present in the name, the compound is ionic. (Exception: some polyatomic ion names always contain prefixes (such as dichromate) but those will be memorized and recognized as ions.)
Writing Formulas for Ionic Compounds Formulas for ionic compounds are written by balancing the positive and negative charges on the ions present. The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s). Polyatomic ion names must still be recognized from memory (e.g. ammonium nitrate), but metals will have a Roman numeral associated with them if there is the possibility of more than one ion (e.g. copper (I) chloride or copper (II) chloride). The Roman numeral indicates the charge on the ion not the number of ions in the formula.
Writing Formulas for Ionic Compounds (continued) Helpful Rules to Remember NameReasoningFormula ammonium sulfate NH 4 has a 1+ charge & SO 4 has a 2- charge, so 2 ammonium ions are required for each sulfate. (NH 4 ) 2 SO 4 zinc chloride Zn has a 2+ charge & Cl has a 1- charge, so 2 chloride ions are required for each zinc ion. ZnCl 2 copper (II) phosphate Cu has a 2+ charge & PO 4 has a 3- charge, so 3 copper (II) ions are required for every two phosphate ions. Cu 3 (PO 4 ) 2 Examples A metal ion is always positive. The Roman numeral indicates the charge, not the subscript. The positive and negative charges must cancel (total charge must = 0). If more than one polyatomic ion is needed, put it in parentheses, and place a subscript outside the parentheses.
Writing Formulas for Covalent Compounds The names of covalent compounds contain prefixes that indicate the number of atoms of each element present. Remember: The compounds named in this way are binary covalent compounds (they contain only two elements, both of which are nonmetals). When in covalent compounds, atoms do not have charges. Subscripts are determined directly from the prefixes in the name. If no prefix is present on the name of the first element, there is only one atom of that element in the formula (its subscript will be 1). A prefix will always be present on the name of the second element. The second element will use the form of its name ending in
Writing Formulas for Binary Covalent Compounds: Examples nitrogen dioxide NO 2 diphosphorus pentoxide P2O5P2O5 xenon tetrafluoride XeF 4 sulfur hexafluoride SF 6 1mono 2di 3tri 4tetra 5penta 6hexa 7heptaa 8octa 9nona 10deca * Second element in ‘ide’ from * Drop –a & -o before ‘oxide’
Writing Formulas: Practice carbon tetrafluorideCF 4 Na 3 PO 4 sodium phosphate Cu 2 SO 4 copper (I) sulfate AnalysisIf “Yes” The compound is covalent: the prefixes give the subscripts. * Are there prefixes present The compound is ionic: subscripts must be determined by balancing charges prefixes covalent prefixes indicate subscripts metal ionic balance charges 3 Na 1+ needed for 1 PO 4 3- metal present ionic balance charges 2 Cu 1+ needed for 1 SO 4 2- Al 2 S 3 aluminum sulfide metal present ionic balance charges 2 Al 3+ needed for 3 S 2- N 2 O 5 dinitrogen pentoxide prefixes covalent prefixes indicate subscripts NH 4 NO 3 ammonium nitrate polyatomic ion present ionic balance charges 1 NH 4 1+ needed for 1 NO 3 1- PbO 2 lead (IV) oxide metal present ionic balance charges 1 Pb 4+ needed for 2 O 2- Fe 2 (CO 3 ) 3 iron (III) carbonate metal present ionic balance charges 2 Fe 3+ needed for 3 CO 3 2-
Chemical Equations and Chemical Reactions During the late eighteenth century, Antoine Lavoisier conducted numerous experiments that involved chemical reactions. His belief in the need to make accurate measurements resulted in precise values for the masses of the substance in his experiments. Based on numerous observations of the same results, Lovoisier wrote his version of the law of conservation of mass: in every chemical reaction, there is an equal quantity of matter before and after the reaction.
Chemical Equations and Chemical Reactions A chemical equation describes what happens in a chemical reaction. The equation identifies the reactants (starting materials) and products (resulting substance), the formulas of the participants, the phases of the participants (solid, liquid, gas), and the amount of each substance. Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products. The quantities are expressed as grams or moles.
Writing Chemical Equations It takes practice to be able to write balanced equations. There are essentially three steps to the process: 1. Write the unbalanced equation. Chemical formulas of reactants are listed on the left-hand side of the equation. Products are listed on the right-hand side of the equation. Reactants and products are separated by putting an arrow between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions. H 2 + O 2 → H 2 O
Writing Chemical Equations 2. Balance the equation. Apply the Law of conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product. Once one element is balanced, proceed to balance another, and another, until all elements are balanced. Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.. 2H 2 + O 2 → 2H 2 O
Writing Chemical Equations 3. Indicate the states of matter of the reactants and products. Use (g) for gaseous substances. Use (s) for solids. Use (l) for liquids. Use (aq) for species in solution in water. Write the state of matter immediately following the formula of the substance it describes. 2H 2 (g) + O 2 (g) → 2H 2 O(l)