The first to recognize these regularities was the German chemist Johann Wolfgang Döbereiner who, in 1829, noticed a number of triads of similar elements:Some triads Element Atomic massDensity chlorine 35.5 0.00156 g/cm3 bromine 79.9 0.00312 g/cm3 iodine 126.9 0.00495 g/cm3 calcium 40.1 1.55 g...
Copper, silver, gold, mercury, tin, lead, and other elements have been known since ancient times and were used to make jewelry, coins, and tools. Phosphorus became the first element to be discovered by Hennig Brand in 1649. It is known as the first scientific discovery of a chemical eleme...
This number became known as an element’s atomic number. 后来,这个数字被称为元素的原子序数。 Today, elements on the periodic table are arranged by atomic number, which gives a more accurate understanding of element properties. 如今,元素周期表上的元素是按原子序数排列的,这使人们对元素的性质有了...
Use this command with at least one other pattern-matching command, such as host , phone number , or user-id ; using it alone does not result in any matches on the voice class. You cannot use this command if you use the pattern command in the voice class. The pattern command matches...
element. Within an element's box on the periodic table, you can find the atomic number, symbol, name, andatomic masslisted for each element. The data provided by the Periodic Table is extremely useful to scientists in chemistry because it provides scientists with information about the properties...
When Dmitri Mendeleev drew up the periodic table, he grouped elements of similar properties. Based on the number of electrons, a scientist can determine which group to place an element into.This pattern is called a period(or row) on the periodic table. ...
ofisotopesof every element—atoms with the same atomic number but different atomic weights. The chemical properties of the isotopes of an element are essentially the same, and all the isotopes of an element occupy the same place in the periodic system in spite of their differences in atomic ...
Thevalenceof the elements (that is, the number of bonds formed with a standard element) is closelycorrelatedwith position in the periodic table, the elements in the main groups having maximum positive valence, or oxidation number, equal to the group number and maximum negative valence equal to ...
This periodic table of elements provides comprehensive data on the chemical elements including scores of properties, element names in many languages and most known nuclides (Isotopes). Below the table there is a "Periodic Table Sorted By" section with links that will sort chemical elements by vario...
1.1原子与元素 - Atom and Element 原子(atom)是化学变化上的最小粒子(particle), 而尖端物理上会研究原子尺度以下的粒子。 两个或以上的原子可以通过化学键组成分子(molecule)。 原子由中子(neutron)、质子(proton)及电子(electron)组成, 由 proton 与 neutron 组成原子核 atomic nucleus,简称核nucleus。proton 与...