Symmary of properties (Cl) Atomic weight Discoverer (year) Scheele, Carl Wilhelm (1774) Natural form gas (Cl 2) Electron configuration 3 s 2 3 p 5 M.p. These spectra are usefull to identify the elements present in a sample. This results in a characteristic emission line in the spectra (which corresponds to specific wavelengths of light). When an electron in an atom is excited to a higher energy level, it can de-excite by emitting a photon of light with an energy equal to the difference between the two levels. The orbitals are filled in a specific order, starting with the lowest energy orbital and working up.Įach element in the periodic table presents its own unique emission spectra, which is determined by the energy levels of its electrons.

In the electron configuration notation, the letters 's', 'p', 'd', and 'f' represent the different types of atomic orbitals, and the superscripts indicate the number of electrons in each orbital. The electron configuration of an element describes the arrangement of electrons in the atoms of that element, and be used to predict its chemical properties and reactivity. It is a tough plastic, used to make many rigid objects. One of the most widely used plastics, polyvinyl chloride (PVC), contains chlorine. Sodium hypochlorite is used to clean water in swimming pools, while bleaches and other cleaners use chlorine compounds to kill germs. This acid is a corrosive liquid that corrodes most metals, releasing hydrogen gas. It reacts with hydrogen to form hydrochloric acid, HCl, an industrial cleaner. For example, its compounds are present in many materials, from slippers to chloroform, CHCl 3. Today, chlorine is used in many other ways. Chlorine in its pure form is poisonous, and was used in World War I, as a weapon (soldiers had to wear masks to protect themselves from chlorine gas, Cl 2). The most common chlorine compound is sodium chloride, NaCl (in nature as the mineral halite, or rock salt).Ĭhlorine compounds are important to the body and used by muscles and nerves. It is a highly reactive gas that forms compounds, and does not exist in pure form in nature. It is highly reactive and forms compounds with almost all other elements.Ĭhlorine is named after the Greek word chlóros, meaning “ pale green“, and refers to the color of this gaseous element. It is a highly reactive, yellow-green gas that belongs to the halogen group in the periodic table. Definition of terms in the previous tableĬhlorine is a chemical element with the symbol Cl and atomic number 17.This fact has key implications for the building up of the periodic table of elements. The ordering of the electrons in the ground state of multielectron atoms, starts with the lowest energy state (ground state) and moves progressively from there up the energy scale until each of the atom’s electrons has been assigned a unique set of quantum numbers. It is the Pauli exclusion principle that requires the electrons in an atom to occupy different energy levels instead of them all condensing in the ground state. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10 -19 coulombs. The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. The total number of protons in the nucleus of an atom is called the atomic number (or the proton number) of the atom and is given the symbol Z. In the periodic table, the elements are listed in order of increasing atomic number Z.

The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. The configuration of these electrons follows from the principles of quantum mechanics.

The chemical properties of the atom are determined by the number of protons, in fact, by number and arrangement of electrons. There is a recurring pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties. Generally, within one row (period) the elements are metals to the left, and non-metals to the right, with the elements having similar chemical behaviours placed in the same column.Įvery solid, liquid, gas, and plasma is composed of neutral or ionized atoms. It is organized in order of increasing atomic number. The periodic table is a tabular arrangement of the chemical elements.

Number 17 periodic table