The word "periodic" comes from the fact that there are repeating trends, or periodicity, as you move across a period. Elements in the periodic table are grouped into rows, which are called periods. The periodic table also shows each element's atomic number and relative atomic mass. For example, copper is represented as Cu, calcium as Ca, and carbon as C. Elements are represented in the periodic table by their chemical symbols, which are one or two-letter abbreviations unique to each element. This number of protons determines the element's number of electrons, which is what makes each element unique. Each element is a pure chemical substance made up of atoms with the same number of protons in their nuclei. Let's take a closer look at how the periodic table is structured.Įlements are the building blocks of the periodic table. This organisation makes it possible to predict how elements behave and react simply by knowing their position in the table. Valence electrons: The electrons in the highest occupied principal energy level of an atom.The periodic table is a useful tool because it organises elements into rows and columns based on their properties. Inner-shell electrons: Those electrons that are not in the outer shell and are not involved in the reactivity of the element. The periods (rows) of the periodic table indicate the number of shells that surround a nucleus.The group numbers (columns) of the periodic table indicate the total number of outer electrons in the valence shell.Valence electrons govern many chemical properties, reactivity, and bonding.Valence electrons are the outermost electron in an electron configuration.These are named after the orbitals, so there is an s-block, p-block, d-block and f-block.Ĭhemistry Question Pack Passage 19 Question 106 The periodic table can be broken up into different blocks based on which orbitals their valence electrons occupy. Thus, group number is a good predictor of how reactive each element will be. Group 1 elements have just one valence electron while group 18 elements have eight (except for helium which has only two electrons total). In general, the number of valence electrons is the same within a column and increases from left to right within a row. Similarly, an element’s column number gives information about its number of valence electrons and reactivity. In addition, the position of an element in the periodic table-its column, or group, and row, or period-provides useful information about how those electrons are arranged.Ĭonsidering the first three rows of the table, each row corresponds to the filling of a different electron shell: helium and hydrogen place their electrons in the 1n shell, while second-row elements like Li start filling the 2n shell, and third-row elements like Na continue with the 3n shell. In a neutral atom, the number of electrons will equal the number of protons. Remember, elements are placed in order on the periodic table based on their atomic number. Inner-shell electrons are not involved directly in the element’s reactivity or in the formation of compounds. In general, atoms are most stable and least reactive when their outermost electron shell is full. Valence electrons, the electrons in the outermost or valence shell, are important as they provide insight into an element’s chemical properties and are the ones gained, lost, or shared during a chemical reaction. The properties of an atom relate directly to the number of electrons in various orbitals. Valence electrons are the electrons in the highest occupied principal energy level of an atom.Įlements are organized by period and group, with the period corresponding to the principal energy level and the group relating to the extent the subshells are filled.
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