1. Are radioactive isotopes helpful or harmless?
Radioactive can be helpful but also very dangerous for us. They are used in medicine to diagnose different sicknesses, but they can damage our molecules, especially our DNA.
2. Why a water strider can walk on water without sinking?
The water has cohesion and adhesion. These two help water to be able to hold very little object on its surface.
3. Why does ice stay on top of water?
Ice stays on top of water because of it is less dense than the liquid water. The hydrogen bonds in ice are stable, but the ones in water constantly break up and re-form.
Five main facts from the reading:
1. The four main elements found in humans are oxygen, carbon, nitrogen, and hydrogen. They make 96.3% of the human body weight.
2. Trace elements are elements found in the human body, but only in minute quantities. They are calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium.
3. Iron is needed by the human body, so it might be found in some food, such as some cereals.
4. Atoms can be joined into molecules through covalent, ionic, or hydrogen bonds.
5. Heat and temperature are two different things. The first one is the amount of energy associated with the movement of atoms and molecules in a body of matter. The second one measured the intensity of hear - that is, the average speed of molecules rather than the total amount of heat energy in a body of matter.
Diagram:
This diagram represents an atom. The white empty circles are the neutrons. The circles with positive signs inside are the protons. And the little circles with the negative signs are the electrons. The protons and neutrons are located in the nucleus of the atom.
Summary:
The introduction page of this chapter talks about the so called "devil's gardens" and the special kind of ants living in there. These ants prevent the growing of many kinds of plants by injecting intruders with a poisonous chemical.
The first main things we learned about in this chapter were the elements, atoms and molecules. We learned that matter is everything that occupies space and has mass. We learned that an element is a substance that cannot be broken down by chemical means, and that the four main elements in the human body are oxygen, hydrogen, nitrogen, and carbon. Trace elements are elements that our body needs to work properly. They do not make up much of our body, but we need them, so they are common additive to food and water. Elements can combine to form compounds. For example sodium and chlorine can be combined to produce sodium chloride or table salt. An atom is the smallest unit of matter that still retains the properties of an element. Atoms are consisted of protons, which have positive charge, neutrons, which do not have any charge, and electrons, which have negative charge. The protons and neutrons are located in the nucleus of the atom. Every element has an atomic number, which is represented by the numbers of protons. Every atom has a mass number, which is represented by the sum of protons and neutrons. Some elements have isotopes. An isotope is an element with same atomic number, but with different mass numbers. Some isotopes are radioactive. Radioactive isotopes can be helpful, but also harmless.
Electrons occur only at certain energy levels, called electron shells. Atoms join into molecules by chemical bonds. They are three different types of bonds Ionic bonds, where an electron from one atom goes to another atom, covalent, where electrons are shared by elements, and hydrogen, where atoms attracted based on their charge. The covalent bond is the strongest bond, and the hydrogen bond is the weakest one. The hydrogen bonds can be nonpolar covalent bonds and polar covalent bonds. An atom's attraction for shared electrons is called its electronegativity. After this we learned that ice is less dense than liquid water, because the molecules in the ice are stable, and the ones in the liquid water are constantly moving, breaking, and re-forming. We also learned that water os the solvent of life. A solution is a liquid consisting of a uniform mixture of two or more substances. After this we read about that the chemistry of life is sensitive to acidic and basic conditions. We use the pH scale to describe how acidic or basic a solution is.
The least few things we learned were that acid precipitation and ocean acidification threaten the environment. Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6. The search for extraterrestrial life centers on the search for water. The last topic of the chapter was taught us that chemical reactions make and break bonds, changing the composition of matter.
Key Terms:
1.Matter - anything that occupies space and has mass.
2.Element - a substance that cannot be broken down to other substances by ordinary chemical means.
3.Compound - a substance consisting of two or more different elements combined in a fixed ratio.
4.Proton - a subatomic particle with a single positive electrical charge (+).
5.Elecron - a subatomic particle with a single negative electrical charge (-).
6.Atomic number - the number of protons in an element.
7.Mass number - the sum of the protons and neutrons in an element's nucleus.
8.Isotope - has the same number of protons and electrons and behaves identically in chemical reactions, but has different number of neutrons.
9.Adhesion - the clinging of one substance to another.
10.Base - a compound that accepts hydrogen ions and removes them from solution.
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