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The periodic table is a system that scientists use to organize and classify chemical elements.
元素周期表是科学家用来记录和分类化学元素的系统。
Originally, many scientists tried to sort the elements by properties.
最初，许多科学家试图按性质对元素进行分类。
One of the early models of the periodic table arranged elements by atomic weight, which naturally grouped elements with similar properties together.
有种早期的元素周期表按原子量来排列元素，自然就将性质相似的元素放在一起了。
However, certain elements were outliers, and did not fit in their groups.
然而，某些元素是“异类”，与周边元素的性质并不相似。
In 1898, a scientist named J.J. Thomson discovered the electron, a subatomic particle with a negative charge.
1898年，科学家J．J．汤姆逊发现了电子，那是一种带负电荷的亚原子粒子。
Later, in 1911, a scientist named Ernest Rutherford learned that electrons orbit a nucleus, which makes up most of the atom’s mass.
后来，在1911年，科学家欧内斯特·卢瑟福了解到，电子围绕原子核运行，而原子的大部分质量都集中在原子核上。
Inside the nucleus, there are protons, which have a positive charge.
原子核内部有带正电荷的质子。
An atom has an equal number of electrons and protons.
原子有相等数量的电子和质子。
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更准确的理解。
