CHEMISTRY (AHS 111) Past Paper (PDF)

‫بسم هللا الرحمن الرحيم‬ Faculty of Applied Health Sciences Technology CHEMISTRY (AHS 111) (1st level, 1st semester) (2) ‫ حجاج حسن‬/‫دكتور‬ Which two of these elements would you expect to show t...

‫بسم هللا الرحمن الرحيم‬ Faculty of Applied Health Sciences Technology CHEMISTRY (AHS 111) (1st level, 1st semester) (2) ‫ حجاج حسن‬/‫دكتور‬ Which two of these elements would you expect to show the greatest similarity in chemical and physical properties: B, Ca, F, He, Mg, P? Locate Na (sodium) and Br (bromine) in the periodic table. Give the atomic number of each and classify each as metal, metalloid, or nonmetal. Give the chemical symbol, including superscript indicating mass number, for the ion with 22 protons, 26 neutrons, and 19 electrons Which of these compounds are molecular: CBr4, FeS, P4O6, PbF2?  Atomic Structure: Electron Configurations Orbitals are Probabilities An orbital is a three-dimensional region around the nucleus where there is a high probability of finding an electron. Electrons are distributed into different atomic orbitals. s-orbitals p-orbitals  Orbitals and Shells Orbitals are grouped in shells of increasing size and energy Different shells contain different numbers and kinds of orbitals Each orbital can be occupied by two electrons First shell contains one s orbital, denoted 1s, holds only two electrons Second shell contains one s orbital (2s) and three p orbitals (2p), eight electrons Third shell contains an s orbital (3s), three p orbitals (3p), and five d orbitals (3d), 18 electrons  Ground-state electron configuration of an atom lists orbitals occupied by its electrons. Rules: 1. Lowest-energy orbitals fill first: 1s → 2s → 2p → 3s → 3p → 4s → 3d (Aufbau (“build-up”) principle) 2. Electron spin can have only two orientations, up  and down . Only two electrons can occupy an orbital, and they must be of opposite spin (Pauli exclusion principle) to have unique wave equations 3. If two or more empty orbitals of equal energy are available, electrons occupy each with spins parallel until all orbitals have one electron (Hund's rule). Energy level Number of electrons 2p2 Type of orbital  Ineratomic bonds CHEMICAL BONDS: THE OCTET RULE In forming compounds, atoms gain, lose, or share electrons to give a stable electron configuration characterized by 8 valence electrons. 1- Ionic bond 2- Covalent bond 1- Ionic Bonding (common in inorganic compounds) - Bond between ions whose charges attract each other - One atom gives electrons and one atom takes electrons (electron transfer). Example NaCl and LiF 2- Covalent Bonding - two atoms sharing electrons within a molecular orbital. COVALENT MOLECULES AND THE OCTET RULE H2 H. +.H H:H or H H Practice Questions Sample Exercise Using Ionic Charge to Write Formulas for Ionic Compounds Write the formula for the compound formed by (a) Na+ and PO43– (b) Zn2+ and SO42– (c) Fe3+ and CO32–  Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: ✓ The charge on the cation becomes the subscript on the anion. ✓ The charge on the anion becomes the subscript on the cation. ✓ If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor. Common Anions Common Cations Polyatomic Ions to Memorize Sulfate Phosphate Ammonium Carbonate Nitrate Hydroxide Acetate  Inorganic Nomenclature Write the name of the cation. If the anion is an element (e.g. chlorine, fluorine) , change its ending to -ide; if the anion is a polyatomic ion (e.g. sulphate, carbonate), simply write the name of the polyatomic ion. If the cation has two or more types of cations (e.g. Mn+2, Mn+3, Mn+4), write the charge as a Roman numeral in parentheses (e.g. Mn(II), Mn(III) and Mn(IV). Patterns in Oxyanion Nomenclature When there are two oxyanions involving the same element (e.g.: SO3-2, SO4-2): The one with fewer oxygens ends in -ite NO2− : nitrite; SO32− : sulfite The one with more oxygens ends in -ate NO3− : nitrate; SO42− : sulfate Practice Questions Sample Exercise Determining the Names of Ionic Compounds from Their Formulas Name the ionic compounds (a) NH4Br, (b) Cr2O3, (c) Co(NO3)2. Give the chemical formulas for (a) magnesium sulfate (b) silver sulfide (c) lead(II) nitrate Nomenclature of Binary Compounds A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however) : - CO is named carbon monoxide not monocarbon monoxide. e.g: CO2 carbon dioxide - SO2 Sulfur dioxide - SO3 Sulfur trioxide Practice Questions Sample Exercise Relating the Names and Formulas of Binary Molecular Compounds Name the compounds (a) SO2, (b) PCl5, Give the chemical formulas for (a) silicon tetrabromide Nomenclature of Organic Compounds Organic chemistry is the study of carbon. Organic chemistry has its own system of nomenclature. The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes. Alkanes ▪ Hydrocarbons contain only C and H. ▪ Alkanes are hydrocarbons that contain only single bonds and are referred to as saturated hydrocarbons. ▪ The general formula for an alkane is CnH2n+2, where n is any positive integer. ▪ Alkanes comprise a homologous series, a group of compounds in which each member differs from the next by a –CH2– group.  Naming Organic Compounds ▪ The name of any organic compound is comprised of three portions: PREFIX + ROOT + SUFFIX ▪ The root name of the compound is determined from the number of C atoms in the longest continuous chain. ▪ The suffix indicates the type of organic compound and is placed after the root. The suffix for an alkane is –ane. The prefix identifies any groups attached to the main chain. When a hydrogen in an alkane is replaced with other an atom or group of atoms (a functional group), the name is derived from the name of the alkane. The ending denotes the type of compound. An alcohol ends in -ol. Roots Number of C Atoms meth- 1 eth- 2 prop- 3 but- 4 pent- 5 hex- 6 hept- 7 oct- 8 non- 9 dec- 10