TEAS: S.3.1 Recognize basic atomic structure

Elements and atoms

There are 118 known elements. 92 of these occur naturally, while the rest have been constructed by scientists in the labs. Carbon, Hydrogen, Oxygen, and Nitrogen make up the majority of living organisms. Every element has its own characteristic identity that determines how it will interact with other elements. These chemical properties depend on the structure of an elements smallest unit: the atom.

Periods

Periods are numbered from top to bottom, starting with the number one, and indicate the shell number that is the valence shell. Period numbers are also the same as the number of sub-shells within each shell. Therefore, shell number 2 is the valance shell of an element in the second period, and that shell contains on subshell of s orbitals and one subshell made up of three p orbitals. Likewise, elements in period 3 have three subshells: Subshell s, subshell p, subshell d. The number of elections in an atom of a period 3 element determines the number of orbitals occupied within each subshell.

Elements and atoms

The atoms of each element have distinct configurations that give the element unquote chemical and physical properties. Where an element is represented on the periodic table is indicative of its number of protons, valence shell configuration, and chemical and physical properties.

Isotopes and Ions

The number of protons in an atom (atomic number) determines its identity as an element. Calculations of atomic mass for an element reveal that it's atoms do not always have the same number of neutrons and protons. Versions of the same element with different number of neutrons are isotopes of each other. Ex. Carbon-12 has six protons and six neutrons while carbon-14 has six protons and eight neutrons In addition, to atoms of the same element having different numbers of neutrons, they can have different numbers of electrons. In an atoms neutral state, the number of protons and elections are equal. Therefore, the whole number (integer) in an element's box on the periodic table also indicates the number of electrons in an uncharged atom of that element.

Ionic and covalent bonds

There is a substantial difference in the chemical and physical properties of an ion compared to the neutral atomic form of the same element. Reactions of metals and nonmetals form compounds with the ionic bonds. Ionic bonds: occur when the metal transfers electrons to nonmetal. However, reactions between nonmetals result in the sharing of elections to form covalent bonds ex. Two oxygen atoms.

Ions

When the number of protons and electrons are not equal in an atom, the atom has a charge and is considered to be an ion. Since protons do not leave an atoms nucleus, the only way that an atom can develop one or more full charges is by either gaining or losing electrons. Cation: If a neural atom loses one or more electrons, the positive charge of its proton "shows through". As a result the charge of the ion is positively charged and called a cation. Typically, metals that are on the left side of the periodic table lose electrons when they form ions. Anion: if a neutral atom gains one or more electrons, it becomes a becomes a negatively charged ion called an anion. The elements in the upper right of the periodic table, the nonmetals, often gain elections to form anions.

Atom

Atom contains three primary components: Electrons Neutrons Protons. These are known as the subatomic particles. Electrons are negatively charged subatomic particles that move around the center of an atom in their orbitals. Each orbital can hold two electrons and orbitals group together to make up a shell. Within shells, orbitals are arranged into subshells labeled s, p, d, f. Where s subshells are closest to the nucleus. The number of orbitals and shells that an elements atom contains depends on the number of electrons within the atoms. Elections in an atoms outermost shell are called valence electrons and include the electrons involved in bonding between atoms. Atoms are in their most stable state when their valence shells are filled. Apart from hydrogen and helium, an atoms valence shell is full when it contains eight electrons. In the center of the atom, the atomic nucleus, are subatomic particles without a charge called neutrons. Subatomic particles that have a positive charge are called protons also in the nucleus.

Columns

Columns on the periodic table correspond to configurations of element's electrons in their valence shell. Each column (group) contains elements that similar chemical and physical properties. There are two ways that groups are labeled on periodic tables. The traditional way labels the groups with Roman numerals and the letter "A" or "B". When looking at periodic table labeled this way, the number of valence electrons for an element in an "A" group is the same as its Roman numeral. Note that in the above periodic table, the modern way of labeling groups has them numbered one through 18 from left to right. Therefore, to determine the number of valence electrons for the last six groups, 10 must be subtracted from its modern number label.

Atom

Fundamental constituent of matter that retains the properties of an element. Atoms properties can be inferred by its position on the periodic table which relates to the number of valence electrons in its outermost shells.

Organization of the periodic table

In the periodic table, a chart that organizes elements by their chemical properties (and correspondingly, their atomic number and electron configuration), each element has its own box indicating it's name with a universally recognized abbreviation. Ex. The abbreviation for the element iron is Fe, and the element called sodium is Na. Two other common pieces of info shown within the elements box are its atomic number and it's atomic mass.

Atomic number

Is the number of protons in one atom of an element. It is consistent to every atom of a particular element. The periodic table arranges elements by increasing atomic number, starting at the upper left-hand corner . Within the same row (period), as one observes boxes to the right, each box contains info about an element that has one more proton per atom.

Atomic mass

Is the sum of the mass of protons and neutrons in one atom of an element. In the periodic table, atomic mass is displayed as a measurement of atomic mass unit (amu). Each proton has a mass of one amu, and each neutron has a mass of one amu. Electrons have such a slight mass that they are not included in the calculation for an elements atomic mass. The decimal component of the atomic mass is the result of averaging atomic versions of an element that differ in their number of neutrons.