Water Science and the Environment

Size: px

Start display at page:

Download "Water Science and the Environment"

Chad Houston
5 years ago
Views:

1 Water Science and the Environment HWRS 201 Dr. Zreda Mr. Ghasemian Fall 2015

2 What is water? A cup of water is an enormous number of H 2 O molecules, each made of 2 atoms of hydrogen and one of oxygen.

3 What are atoms? Atoms are the building blocks of nature. Matter with which we interact in nature is made of atoms. Each atom consists of a small, relatively heavy nucleus and a number of really small, really light electrons. The nucleus is made up of protons, which have a positive electrical charge and neutrons, which don t have a charge. All we care about are the electrical properties of hydrogen and oxygen because bonds between atoms are what form molecules, so we won t worry about neutrons for now. Hydrogen Oxygen

5 The oxygen and hydrogen atoms are incomplete The oxygen atom has 8 protons, and the hydrogen atom has 1. Usually atoms have as many electrons as they have protons, so the ordinary oxygen atom has 8 electrons and the ordinary hydrogen atom has 1. That s not stable! Hydrogen Oxygen

6 Electron shells The electrons of all atoms float around their nucleus in shells so an atom looks a bit like the solar system where the sun is the nucleus and the planets are electrons. Iron Atom

7 The rule of shells It s a fact of nature that atoms want to have 2 electrons in their innermost shell and 8 in the second shell. The general rule is that atoms can have a limited number of electrons per shell Shell Number Maximum # of electrons Iron Atom Atomic Number: 26 Shell occupation: 2, 8, 14, 2 n 2 x n 2

8 Outer shells of O and H Since the hydrogen atom has only one shell and that shell only contains one electron, it wants another electron. Similarly, an oxygen atom has only six electrons in its outer shell, so it wants two more electrons. Hydrogen Oxygen

9 The water molecule: a perfect match Atoms can get their missing electrons by sharing. The combination of two hydrogen atoms with one atom of oxygen satisfies all parties! The oxygen atom gets the two electrons it s missing, and each hydrogen atom gets the electron it s missing. Since the water molecule makes all its atoms complete, the water molecule is stable. Shared electrons

10 The water molecule: a perfect match The shared electrons form powerful covalent bonds between the oxygen and hydrogen atoms. They hold the water molecule together. Strong bonds formed by shared electrons

The water molecule: polarity The shared electrons

slight positive charge because there aren t any

The oxygen side with the unshared electron pairs

11 The water molecule: polarity The shared electrons give the hydrogen side of the water molecule a slight positive charge because there aren t any electrons there. The oxygen side with the unshared electron pairs are slightly negative. The separation into positive and negative sides is called polarity

That s what makes molecules in liquid water hold together.

12 Holding liquid water together Polarity allows water molecules to form another kind of bond, a hydrogen bond between water molecules. That s what makes molecules in liquid water hold together. The weak bonds are what let water act as a liquid. These hydrogen bonds are times weaker than the strong covalent bonds.

13 Physical properties of water Water can exist in three states Ice, if the temperature is less than 0 degrees C Liquid, if the temperature is between 0 and 100 degrees C Vapor, single molecules of water. Water can hold more heat than any other liquid (except liquid ammonia) This is why the oceans are so good at stabilizing the temperatures of coasts and islands. Water is a great solvent More substances dissolve in greater amounts in water than in any other liquid (but oil doesn t). This is due to the polar nature of the water molecule. The strong hydrogen bonds give water a high surface tension. So raindrops are spherical.

14 Molecular structure and the states of water Ice Liquid Vapor

15 Surface tension

Takeaway: What is liquid water? Even a small drop of water contains a huge number of H2O molecules. The molecules in a drop are held together by weak bonds.

16 Takeaway: What is liquid water? Even a small drop of water contains a huge number of H2O molecules. The molecules in a drop are held together by weak bonds. Weak hydrogen bonds make it easy to separate a drop into smaller drops. A single H2O molecule is held together by sharing electrons between its oxygen and hydrogen atoms. Covalent bonds hold the hydrogen and oxygen atoms together in a molecule of water. Hydrogen bonds hold water molecules together in its liquid form.

Water is one of the few compounds found in a liquid state over most of Earth s surface.

The Water Molecule Water is one of the few compounds found in a liquid state over most of Earth s surface. Like other molecules, water (H2O) is neutral. The positive charges on its 10 protons balance out