![]() These ideas can be extended to calculate the formula mass of a substance by summing the average atomic masses of all the atoms represented in the substance’s formula. ![]() Formula MassĪn earlier chapter of this text described the development of the atomic mass unit, the concept of average atomic masses, and the use of chemical formulas to represent the elemental makeup of substances. Understanding the relationship between the masses of atoms and the chemical formulas of compounds allows us to quantitatively describe the composition of substances. For example, Dalton’s atomic theory was an attempt to explain the results of measurements that allowed him to calculate the relative masses of elements combined in various compounds. ![]() Many argue that modern chemical science began when scientists started exploring the quantitative as well as the qualitative aspects of chemistry. Explain the relation between mass, moles, and numbers of atoms or molecules, and perform calculations deriving these quantities from one another.Define the amount unit mole and the related quantity Avogadro’s number.Calculate formula masses for covalent and ionic compounds.Metallic character decreases from left to right in each period of the periodic table.By the end of this section, you will be able to: Metallic character increases down a group. Going down a group, the atomic radius increases: the outer electrons are farther from the nucleus and are easier to remove, thus increasing the metallic character.The metallic character is essentially the ease with which an atom gives up an electron Metalloid: an element with properties intermediate between metals and nonmetals. Metalloids divide the periodic table in a zigzag line between metals on the left and nonmetals on the right.Nonmetal: poor conductor of heat and electricity. They are generally softer elements, often colored, with lower melting and boiling points than most metals.Metal: good conductor of heat and electricity. They tend to be hard, metallic-looking solids with high melting and boiling points. The majority of elements are metals.Most elements can be classified as metals or nonmetals based on their ability to conduct heat and electricity: ⇒ very stable elements, generally considered to be inert gases Noble gases: last column = helium, neon, argon, (krypton, xenon, radon).⇒ colorful and corrosive nonmetals, very reactive Halogens: penultimate column = fluorine, chlorine, bromine, iodine, (astatine).⇒ react with O 2, less reactive to water than alkali metals Alkaline-earth metals: 2 nd column = beryllium, magnesium, calcium, (strontium, barium, radium).⇒ very reactive metals and can explode if they are exposed to water Alkali metals: 1 st column = lithium, sodium, potassium, (rubidium, caesium and francium).Several groups of representative elements are known by common names: The top-row elements are called lanthanides and the bottom-row elements are actinides The inner transition metals: elements in the 2 rows at the bottom of the table.The transition metals: elements in the groups between the elements of the main group (groups 3-12).The main-group elements: elements in the 2 groups on the far left and the 6 groups on the far right of the periodic table (groups 1, 2, 13-18). ![]() Members of the same group have the same number of electrons in the outermost shells of their atoms and form bonds of the same type. Here He Lies Beneath Bed Clothes, Nothing On, Feeling Nervous, Naughty Mar gret Always Sighs, " Please Stop Clowning Around "Ī vertical column of elements is called a group. ![]() 3 rd period: Na, Mg, Al, Si, P, S, Cl, Ar.You should generally know the first 3 periods: A period forms a row of the periodic table. The chemical elements have a periodic pattern when they are arranged in ascending order of atomic number. Each vertical column corresponds to a group of elements with the same properties, each horizontal line corresponds to a periodĮach element of the periodic table is represented by a tile containing the name of the element (chemical symbol composed of one or two letters), the atomic number and the average mass (usually indicated with 4 significant figures) The elements are arranged by atomic number. A chart of 118 elements first published by Dmitri Mendeleev in 1869, in which elements with similar chemical and physical properties are grouped. ![]()
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