As of June 2002, astronomers had discovered more than
100 other planets orbiting distant suns. With advances in tech-
nology, that number will surely increase during the opening
decades of the twenty-first century. Although our explorations
of the Cosmos hold great promise of future discoveries, among
all of the known worlds, Earth remains unique. Thus far it is the
only known planet with blue skies, warm seas, and life.
Tài liệu tham khảo giáo trình nhôm trong thiết kế xây dựng - Chương 1 About aluminium
1.1 GENERAL DESCRIPTION
1.1.1 The element
Aluminium is a metallic element having the chemical symbol Al, with
atomic number 13 and atomic weight 27. The nucleus of the atom contains
13 protons and 14 neutrons (a total of 81 quarks). Aluminium is the
third most common element in the earth’s crust, coming after oxygen
and silicon. It makes up 8% of the crust’s total mass and is the most
Chapter 2 - The chemical context of life. In this chapter, you should now be able to: Identify the four major elements; distinguish between the following pairs of terms: neutron and proton, atomic number and mass number, atomic weight and mass number; distinguish between and discuss the biological importance of the following: nonpolar covalent bonds, polar covalent bonds, ionic bonds, hydrogen bonds, and van der Waals interactions.