General Chemistry CHEM 100: Atoms Molecules and Ions PDF

GENERAL CHEMISTRY CHEM 100 Chapter -2 Atoms Molecules and Ions Prepared by Mrs. Munfis Patel 1 @Mrs. Munfis  Learning Objectives At the end of the Chapter, st...

GENERAL CHEMISTRY CHEM 100 Chapter -2 Atoms Molecules and Ions Prepared by Mrs. Munfis Patel 1 @Mrs. Munfis  Learning Objectives At the end of the Chapter, students will be able to… ⚫* Identify the type of substance/compound/mixture given a microscopic diagram ⚫*Distinguish between physical and chemical changes/properties ⚫* Identify the following properties of subatomic particles: mass, charge, location in the atom ⚫* Predict no. of protons/neutrons/electron in 𝐴𝑍𝑋𝑛 / Isotopes and Ions ⚫*Classify Molecules/ Ions ⚫*Convert from molecular to empirical formulae ⚫*Know the formula and charge for the most common polyatomic ions 2 @Mrs. Munfis  Chemistry is everything…and Chemistry is – Part of Everything We Do 3 @Mrs. Munfis  Everything in the universe (except energy) is made of matter. Matter is defined as anything that has mass and takes up space. Atoms are the basic units of matter and the defining structure of elements. They contain three types of subatomic particles—protons, electrons, and neutrons. So chemistry is only 3 things… - + Electrons Neutrons Protons 4 @Mrs. Munfis  An atomic representation of the states of matter Real life observations Macroscopic scale Atomic representation Microscopic scale Macroscopic Microscopic 5 @Mrs. Munfis  Definitions for Components of Matter Element - the simplest type of substance with unique physical and chemical properties. An element consists of only one type of atom. It cannot be broken down into any simpler substances by physical or Pure elements: chemical changes. Copper pipe Molecule - a structure that Oxygen gas consists of two or more atoms that are chemically bound together and thus behaves as an independent unit. Can be an element or a “compound” 6 @Mrs. Munfis Definitions for Components of Matter (2) Compound – a substance composed of two or more elements that are chemically combined. Can be covalent or ionic Pure compound: Water Mixture – a group of two or more elements and/or compounds that are physically mixed. Contain more than one substance, not bound in a fixed ratio Sand: A mixture of small rocks 7 @Mrs. Munfis  Mixtures Homogeneous mixtures – components mix evenly. Heterogeneous mixtures-components do not mix evenly. Salt and water Sand and water Homogeneous mixture Heterogeneous mixture Salt mixes evenly with water Sand separates from water 8 @Mrs. Munfis  Matter Pure Substances Mixtures One element or compound More than on substance Elements Compounds Homogeneous Heterogeneous One type of atom Different types of atoms Components are evenly Components are not evenly bound together blended blended 9 @Mrs. Munfis  Describe these samples as a pure element, a pure compound, and a mixture: Sample A Sample B Sample C Pure element Pure compound Mixture Only one type of Two types of atoms Two types of atoms atom present. are present. One of are present, but they each atom binds to do not bond together form a compound. to form a compound. There is only one This is a mixture of compound present. elements. 10 @Mrs. Munfis  Describe these substances as a pure element, a pure compound, a homogeneous mixture, and a heterogeneous mixture: Air Falafel Dry ice (Solid CO2) Gold coin Homogeneous Heterogeneous Pure compound Pure element mixture mixture 11 @Mrs. Munfis  Physical and Chemical Properties Physical Properties: Properties which a substance shows by itself without interacting with another substance. Do not change the identity of the substance Color, melting point, boiling point, density Chemical Properties: Properties which a substance shows as it interacts with, or transforms into, other substances. Change the identity of the substance Flammability, corrosiveness, Combustion 12 @Mrs. Munfis  The Distinction Between Physical and Chemical Change Physical changes: usually easy to reverse Chemical changes: usually hard to reverse Liquid water 13 @Mrs. Munfis  Work with a partner to label the pictures as physical or chemical changes: P P C P P C P C P P P C C P C P 14 @Mrs. Munfis  Atomic Structure All matter consists of very small particles called atom. Atom is the basic unit of an element that can enter into chemical combination. Atoms are composed of tiny nucleus that contains protons and neutrons and revolving round the nucleus are the electrons. nucleus (protons & neutrons) Electron cloud If an atom could be expanded to the size of a football stadium, the nucleus would be the size of a single blueberry. 15 @Mrs. Munfis  Atomic Structure ⚫ An electron is a negatively charged particle with a very small mass. ⚫ A proton is a positively charged particle with a mass 1836 times that of an electron. ⚫ A neutron is an uncharged particle with a mass about the same as that of a proton. 16 @Mrs. Munfis  Dalton’s Theory(1766-1844) ⚫ In the early 1800s, the English Chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms. ⚫ He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles. ⚫ Atoms of the same element are exactly alike. ⚫ Atoms of different elements are different. ⚫ Compounds are formed by the joining of atoms of two or more elements. 17 @Mrs. Munfis  Bohr Model (1913) 1. Electrons orbit the nucleus in orbits that have a set size and energy. 2. The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit. 3. Light is absorbed or emitted when an electron moves from one orbit to another. 4. The number of electrons in any orbit can be calculated by using 2n2 rule. 5. Only principal quantum number is enough to describe this model. 18 @Mrs. Munfis  Atomic Number (Z): is the number of protons found in the nucleus of an atom. Atomic number = number of protons The number of protons determines the identity of the atom. 1 proton – hydrogen 2 protons – helium 3 protons – lithium 4 protons - beryllium In an atom of neutral charge, atomic number is equal to the number of electrons. Atomic number = number of protons or number of electrons Z=P or E 19 @Mrs. Munfis  Mass Number (A): is the total number of protons (Z) and neutrons (N) in the nucleus of an atom. Mass number = number of protons + number of neutrons A = Z+ N=P+N X = Atomic symbol of the element A = Mass number; A = Z + N Z = Atomic number (the number of protons in the nucleus) N = Number of neutrons in the nucleus 20 @Mrs. Munfis  What happens when--------- Change the # of electrons - Add 2 e- This is common! - + + - It’s called “ionization” - because it forms an ion - Change the # of neutrons + Add 2 n0 + - This is very rare! - + Changes to a new + isotope of the same - element Add 2 p+ - This is very rare! Change the # of protons + + + + Changes to a new element - 21 @Mrs. Munfis  Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl 17 17 chlorine - 35 chlorine - 37 ⚫ 17 protons, 17 electrons, and 18 neutrons ⚫ 17 protons, 17 electrons, and 20 neutrons 22 @Mrs. Munfis  Practice Exercise Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______ 23 @Mrs. Munfis  MOLECULES A molecule is an aggregate of at least 2 atoms in a definite arrangement held together by chemical bonds. H2 H2O NH3 CH4 Homo atomic molecule :A molecule containing atoms of the same element. Ex: H2(Hydrogen molecule), N2(Nitrogen molecule), O2(Oxygen molecule) or Hetero atomic molecule : A molecule containing atoms of 2 or more elements in fixed ratio. Ex: H2O(water molecule), NH3(ammonia molecule). 24 @Mrs. Munfis  Diatomic molecule: A molecule containing only two atoms. Ex. Molecules of Hydrogen (H2), nitrogen (N2) , oxygen (O2), Fluorine (F2) and chlorine ( Cl2 ), Hydrogen chloride ( HCl ), Carbon monoxide ( CO ) Polyatomic molecule : Molecules containing more than 2 atoms. Ex:- Water (H2O) , Ozone (O3), ammonia (NH3) etc., 25 @Mrs. Munfis  ⚫A molecular formula/Chemical Formula shows the exact number of atoms of each element in the smallest unit of a substance. ⚫ An empirical formula shows the simplest whole- number ratio of the atoms in a substance. Molecular formula Empirical formula H2O H2O C6H12O6 CH2O O3 O N2H4 NH2 26 @Mrs. Munfis  Ions An ion is an atom, or group of atoms, that has a net positive or negative charge, obtained by removing or adding electrons. For Example: Na+, Cl- Cation – ion with a positive charge. If a neutral atom loses one or more electrons it becomes a cation. Lithium atom: Li Lithium ion: Li+ 3 protons, 3 electrons 3 protons, 2 electrons net charge: 0 net charge: +1 Loses 1 e- Li Li+ Neutral charge +1 charge 27 @Mrs. Munfis  Anion – ion with a negative charge. If a neutral atom gains one or more electrons it becomes an anion. Fluorine atom: F Fluoride ion: F- 9 protons, 9 electrons 9 protons, 10 electrons net charge: 0 net charge: -1 Gains 1 e- F F- Neutral charge -1 charge 28 @Mrs. Munfis  How many protons and electrons are in 27 Al 3+ ? 13 13 protons, 10 (13 – 3) electrons Al → Al3+ +3e- 78 2- How many protons and electrons are in 34Se ? 34 protons, 36 (34 + 2) electrons Se +2e- → Se2- 29 @Mrs. Munfis  A monatomic ion contains only one atom. Examples: Na+, Cl-, Ca2+, O2-, Al3+, N3- Some common monatomic ions of the elements: Cations Anions Charge Formula Name Charge Formula Name +1 H+ hydrogen –1 H– hydride Li+ lithium F– fluoride Na+ sodium Cl– chloride K+ potassium Br– bromide Cs+ cesium I– iodide Ag+ silver +2 Mg2+ magnesium –2 O2– oxide Ca2+ calcium S2– sulfide Sr2+ strontium Ba2+ barium Zn2+ zinc +3 Al3+ aluminum –3 N3– nitride 30 @Mrs. Munfis  A polyatomic ion contains more than one atom. Examples: OH-, CN-, NH4+, NO3- Some Common Polyatomic Ions 31 @Mrs. Munfis