Which are essential elements of life?
About 25 out of 92 natural elements are known to be essential to life. Just 4 of these make up to 96% of living matter:
- carbon (C)
- oxygen (O)
- hydrogen (H)
- nitrogen (N)
The remaining 4% making up a living matter are Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, Magnesium and traces of some other elements.
When do we use radioactive tracers?
Radioactive tracers are important diagnostic tools in medicine. For eg., certain kidney disorders can be diagnosed by injecting small doses of substances containing radioactive isotopes into the blood and then measuring the amount of tracer excreted in the urine. Radioactive tracers are also used in combination w
ith sophisticated imaging instruments, such as PET scanners, which can monitor chemical processes, such as those involved in cancerous growth as they actually occur in the body.
How and what do chemical reactions do to chemical bonds?
Chemical reactions make and break chemical bonds, they change reactants into products. Theoretically, all chemical reactions are reversible, so the bonds can always be made and broken again.
Facts:
- Elements cannot be broken down
chemically to other substances.
- Carbon, oxygen, nitrogen and hydrogen make up to 96% of living matter.
- One of the most serious environmental treats is radioactive fallout from nuclear accidents.
- Electrons exist in orbitals, 3D spaces with specific shapes that are components of electron shells.
- Electrons of a more polar covalent bond are pulled closer to the more electronegative atom.
Summary:
About 25 out of 92 natural
elements are known to be essential to life. Elements cannot be broken down chemic
ally to other substances.
An atom, the smallest unit of an element has a nucleus that is made out of neutrons and protons and electrons. electrons exist in orbitals, 3D spaces with specific shapes that are components of electron shells.
There are different types of c
ovalent bonds shared by two atoms: single/double, polar/non-polar.. Ionic bonds (chemical bonds between oppositely charged ions) form ionic compounds, also called salts (eg. NaCl). NaCl is a product made out of Na and Cl as reactants in a chemical reaction (the making and breaking of chemical bounds, leading to changes in
the composition of matter).
Key Words:
matter = anything that takes up space and has a mass
element = substance that cannot be broken down to any other substance by any chemical reactions
compound = substance consisting in two or more different elements combined in a fixed ratio
atom = the smallest unit of matter that still retains the properties of an element
dalton = atomic mass unit (John Dalton, developed atomic theory, 1800.)
atomic number = number of protons, subscript to the left of the symbol
mass number = sum of the protons and neutrons in the nucleus of an atom, superscript to the left of the symbol
energy = capacity to cause change, especially to do work
orbital = 3D space where electron is found 90% of the time
valence = bonding capacity, usually equals to number of unpaired electrons
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