Author name: Mingdi

A carbon atom possesses four electrons in its outermost orbit. To reach stability, it therefore tends to form four covalent bonds. By sharing these four electrons, it acquires an additional four electrons from other atoms, completing its outermost shell with a total of eight electrons. Atoms that readily share electrons with carbon, thus forming bonds, include hydrogen, oxygen, nitrogen, halogens, and, naturally, other carbon atoms. These bonds are referred to as carbon-carbon bonds, carbon-hydrogen bonds, carbon-oxygen bonds, etc. (Note they are all covalent bonds.)

如果问你的祖父辈，他们听到哪一个国家和民族的老歌时，会挺感动，心灵跟着有所触动，他们很可能会说是俄罗斯民歌。苏联和中国有过一段非常友好的邦交历史，两个国家共同的理想曾让那个时代的青年热血沸腾。后来，苏联解体，成为15 个独立的联邦国，其中最大的联邦国俄罗斯继承了苏联的大部分资源、国力、国际义务和地位。

In the middle of Las Vegas, colors and patterns swirl over the surface of a massive sphere . For a moment, it looks like an alien planet with a bizarre arrangement of ridges, forests, and oceans. But then the swirls change to pinks and blues, as if the planet is having a vivid dream.

eBay（易贝）收购PayPal的交易完成后，员工陆续离职，使PayPal成为硅谷历史上创造创业者群体最多的一家公司。从PayPal走出来的创业者，不仅在互联网行业的原始社会时代就创建了PayPal这样一个互联网金融的先行者，而且他们出来各自创业之后，还创造了一大批耳熟能详的公司。