ALL SOLUTION SOLVED SPRING FALL-2022 EDITION ANSWERS 100% CORRECT AID GRADE A+

Atom The atom is the smallest unit of matter. Every atom contains one nucleus at least one electron. The nucleus contains at least one positively charged proton and an equal number of neutrally charged neutrons. Every atom also has at least one negatively charged electron bound to the nucleus. When the number of protons (the atomic number) is equal to the number of electrons, the atom is neutral. When the number of protons and number of electrons differ, the result is an ion. The way electrons are distributed around an atom or molecule is known as an electron configuration. Electrons are distributed among “shells” which may be thought of as energy levels. The configuration that corresponds to the lowest energy level is called ground state. Every other configuration is considered an excited state. Electrons always fill the lower energy levels first. To write an electron configuration: • Locate the atomic number • If the atom being studied is charged, this should be taken into account. Cations (positively charged) will have fewer electrons in the magnitude of the charge. Anions (negatively charged) will have extra electrons in the magnitude of the charge. • Understand the order of orbitals: o S – 1 single orbital, holds 2 electrons o P – 3 orbitals, holds 6 electrons o D – 5 orbitals, holds 10 electrons o F – 7 orbitals, holds 14 electrons • Fill the orbitals in the following order, according to the number of electrons of the atom being studied. o 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s. • The number of electrons is written in superscript to the right of the orbital letter. For example, the configuration for neutral neon would be written as 1s2 2s2 2p6. Periodic Table The periodic table contains the most important information about all known elements. An element is a substance that is composed purely from one type of atom. The periodic table is broken into four main groups. • Main group elements: active metals in columns (also called groups) 1 and 2 as well as the metals, semimetals and nonmetals in columns 13-18. • Transition metals: the elements that serve as a transition between the two main groups • Lanthanides and Actinides: known as the inner transition metals because their atomic numbers are actually located between the first and second elements in the last two rows (also called periods) of transition metals. Electronegativity is an important concept in chemistry and can be charted predictably across the periodic table. Electronegativity is an atom’s measure of attraction for electrons. • Electronegativity increases from bottom to top within groups • Electronegativity increases from left to right across periods Additional important information about each element can be gathered from the periodic table: • The number of protons in an atom will always determine what element it is from. The number of protons will always be the same for all atoms from the same element. The number of protons is called the atomic number. • The number of electrons, in a neutral atom, is equal to the number of protons. If the atom is an ion, the number of electrons will vary. • The number of neutrons in an atom can also vary. If an atom has a different number of neutrons, it is called an isotope. • The mass number is equal to the number of protons plus the number of neutrons. In order to calculate the number of neutrons, subtract the atomic mass minus the atomic number. • The relative atomic mass, also called the atomic weight, is an average of the atomic masses of all the different isotopes in a sample. Example: Hydrogen’s chemical symbol is H. Its atomic number is 1 and atomic weight is 1.00794. This shows that there are some isotopes of hydrogen. A neutral hydrogen atom would have a mass of 1. Atomic Number Each element has its own atomic number, which is based on the number of protons in an atom. The number of protons will always remain the same for an element. In a neutral atom, the number of protons is equal to the number of electrons. The number of electrons can change based on various reactions that can occur involving them. Example: All atoms with 2 protons are Helium. Subatomic particles An individual unit of an element is called an atom. Atoms cannot be broken into smaller pieces while still maintaining the properties of that element. Atoms get their properties from their subatomic particles. Atoms consist of two regions: the nucleus and the electron cloud. The nucleus is in the center of the atom and contains positively charged protons and uncharged neutrons. This is what makes up the mass of the atom. The electron cloud is a much larger region of the atom; however, the mass is negligible. This region is where electrons are found. Electrons are negatively charged. It is the attraction between the positively charged protons and the negatively charged electrons that holds the atom together. Most atoms have all three of these subatomic particles, except hydrogen, which doesn’t have any neutrons. Chemical Formulas Understanding chemical formulas and how to read them is important. It is the basis for understanding reactions. Consider the equation below: The elements and molecules shown on the left are the reactants. These are the substances used to begin a chemical reaction. After the reaction takes place, it forms products. These are shown on the right side of the equation. The arrow between the two shows that a reaction took place. It always points from the reactants to the products. There is a “(g)” listed after each molecule. This tells the state of matter of the molecule. In this case, all of the molecules are in a gaseous state. It could be a liquid (l), solid (s) or gas (g). Sometimes it will say (aq), which means aqueous. This means that those molecules have been dissolved in water. There is a subscript of 2 with each of the reactants. Subscript means written slightly lower than the rest of the text. A subscript number tells how many atoms of an element are present. In this specific reaction, it takes 2 hydrogen atoms to combine with 2 chlorine atoms. The regular sized 2 in the products is called a coefficient. This refers to how many of an entire molecule there are. In this case, there are 2 HCl molecules made in the reaction. Below are several images to help understand the terms and what they may look like: Molecular Weight The sum of the weight of all the atoms in a given formula equals the molecular weight of the substance. Atoms are measured in atomic mass units (amu). Calculating the molecular weight is important because it is necessary information to determine how many grams are in one mole of a substance. The mole is a unit of measure in chemistry which denotes the quantity of a substance present. To calculate molecular weight: • Determine the number of atoms of each element are present in a substance • Multiply the atomic weight of each element by respective the number of atoms of each element • Add them Stoichiometry (Molar Mass) Molar mass is the standard unit in chemistry. It shows how many grams of a substance are present within 1 mole of that substance. The units for mole are grams/mole. To find the molar mass of a compound: • Determine the quantity of each atom type within the compound - this information is found in the chemical formula • Multiply (number of atoms present)(atomic weight of atom) • Add them and include units Conversions are another important part of stoichiometry. When given a quantity (in either grams or moles) as well as a chemical formula (to solve for the molecular weight), there is enough information to solve for an unknown using the formula: