Atoms and Charged Particles Atoms, Isotopes, Ions and how they interact and form molecules Atoms Atoms are made up of three subatomic particles. Atoms have the same number of protons, neutrons and electrons (except hydrogen, which lacks a neutron). Protons - positively charged Neutrons - neutrally charged (not charged) Electrons - negatively charged Atomic Structure An atomic nucleus is made up of protons and neutrons. Protons and neutrons contribute 99.9% of an atom’s mass (weight). Atomic nuclei are held together by strong nuclear force (one of 4 fundamental forces of physics). This force is strong enough to keep the protons together even though their positive charge naturally drives them apart. Electrons have almost no mass but contribute negative charge. Their negative charge keeps them orbiting around the positive nucleus via electromagnetism (another fundamental force). Electromagnetic force attracts the electrons to the nucleus but doesn’t bond them to it, so they can be stolen or shared by other atoms. Elements Adding or removing a proton changes its atomic number, and thus what element it is. A carbon has six protons. If you removed one it would become boron. If you added one it would become nitrogen. Isotopes Adding or removing a neutron only changes its weight because neutrons have no electromagnetic charge. An atom with more or less neutrons than protons is called an isotope. An isotope of an element with less neutrons would be lighter than a regular atom of the same element. An isotope with more neutrons would be heavier. Ions Most elements have a tendency to lose electrons or take electrons. Some elements are inert, so they do not ionize (become ions). A free floating charged particle. In other words, inert elements are so stable by themselves that they do not interact with other elements (under normal circumstances). An atom has a net neutral charge. But when it ionizes, loses or gains electrons, it will have a net positive charge or net negative charge. Whether an atom gains or loses electrons is specific to each element. Hydrogen has a tendency to lose its electron, so it becomes a more positive. (H⁺) Oxygen has a tendency to gain two electrons, so it becomes more negative. (O²⁻) Chemical Bonding A chemical bond (specifically a covalent bond) is when an atom’s tendency to take electrons causes it to share those electrons with an atom that tends to lose them. The negative electron(s) are caught in the attraction of both atoms’ positive nuclei, thus bonding them together forming molecules. Example 1: Sodium tends to lose one electron (Na⁺) while Chlorine tends to gain one (Cl⁻). If sodium’s electron is caught between them, they form sodium chloride (NaCl), or table salt. Example 2: Oxygen tends to take 2 electrons (O²⁻) and Hydrogen tends to lose its electron (H⁺). Hydrogen only has one electron to give and Oxygen needs two, so it bonds with two hydrogen atoms. These three atoms form H₂O, or water. Polarity and Molecular Charge An atom’s tendency to become either positive or negative carries over to the molecule it is a part of. The interaction of an atom’s electromagnetism (or charge) with other atoms in the molecule determines the electromagnetism of the molecule as a whole. “Polar” is a latin term which has come to mean “extreme” or “opposite.” If a molecule has extremes, meaning one end in positive and the other negative, then it is polar. Like a magnet. If there is no distinct positive or negative end, then the molecule is nonpolar. Examples of Polar and NonPolar Molecules In polar molecules, the charge goes from positive to negative in one direction. This makes one end of the molecule more positive and the other more negative. In nonpolar molecules, the change in charge is distributed, so there is no distinct positive or negative side. Water and Carbon Dioxide Example Water (H₂O) is a polar molecule because the hydrogens on one side are positive and the oxygen on the other side is negative. Carbon dioxide (CO₂) is nonpolar because there is no positive side and negative side of the molecule. The carbon contributes a positive charge and oxygens contribute negative charges. But there is no negative end and positive end. What other differences can you see? Diatomic Molecules “Di-” is the greek prefix for “two.” So a diatomic molecule, is a molecule made of two atoms. There are a group of elements that, when in gas form, become diatomic molecules with other atoms of the same element. They are Bromine, Iodine, Nitrogen, Chlorine, Hydrogen, Oxygen, and Fluorine. (otherwise known as BrINClHOF) Examples: Oxygen forms O₂, Nitrogen forms N₂, Chlorine forms Cl₂, and Hydrogen forms H₂. You might have heard of Ozone (O₃) which is a triatomic molecule. *You only need to know the underlined diatomic molecules for this class* Macro Molecules “Micro” means small and “macro” means large. So a macromolecule is a large molecule. In Biochemistry there are four main categories of macromolecules: -Carbohydrates -Lipids -Amino Acids -Nucleic Acids That’s all for Now! This wraps up the basic chemistry you need to know for Honors Biology. The next slideshow will be on Biochemistry, where we will delve deeper into macromolecules! Here’s a picture of a capybara with a chicken to brighten your day!
