Biology Lesson 2.1: The Nature of Matter PDF

BIOLOGY Lesson 2.1: The Nature of Matter  OBJECTIVES 1. Name and describe the three subatomic particles that make up atoms. 2. Describe how all of the isotopes of an element are similar. 3. Describe the ways that a compound differs from its component elements. 4. Name...

BIOLOGY Lesson 2.1: The Nature of Matter  OBJECTIVES 1. Name and describe the three subatomic particles that make up atoms. 2. Describe how all of the isotopes of an element are similar. 3. Describe the ways that a compound differs from its component elements. 4. Name and describe the main types of chemical bonds.  ATOMS Atom: basic unit of matter ○ Comes from the Greek word atomos, which means “unable to be cut”. ○ Extremely small in size. ○ Made up of three subatomic particles: protons, neutrons, and electrons Protons: positively charged particles (+) Neutrons: particles that carry no charge (neutral) Electrons: negatively charged particles (-) Only 1/1840 the mass of a proton In a constant motion in the shape surrounding the nucleus Arranged in a series of shells or orbitals ○ First shell: can contain no more than two electrons ○ Second shell: can contain no more than 8 electrons  ATOMS Protons and neutrons are held together by strong forces to form the nucleus at the center of the atom. Atoms have equal numbers of electrons and protons--- atoms are electrically neutral because the opposite charges cancel out.  ELEMENTS & ISOTOPES Element: a pure substance that consists entirely of one type of atom ○ Elements are represented by one- or two-letter symbols. Examples: C stands for carbon H stands for hydrogen Na stands for sodium I stands for iodine Atomic number: the number of protons in the nucleus of an atom ○ Example: carbon’s atomic number is 6, so each atom of carbon has six protons and six electrons  ELEMENTS & ISOTOPES There’s nearly 100 naturally occurring chemical elements on Earth, but less than 20 of them are commonly found in living organisms. About 99% of the mass of living things is composed of just six elements: ○ Carbon ○ Calcium ○ Hydrogen ○ Oxygen ○ Nitrogen ○ Phosphorus ○ Remaining 1% are trace elements  ELEMENTS & ISOTOPES When two atoms interact, their shells overlap and may even swap electrons with each other. This affects how they can interact with other atoms and how they participate in chemical reactions. ○ You could say that the number of electrons in the outer shell is the “face” that a particular atom shows to its neighbors. Atoms of the same element that differ in the number of neutrons they contain are known as isotopes. ○ Neutrons affect the atomic mass of an isotope, but they don’t affect its chemical properties--- in other words isotopes have different masses, but their chemical properties are the same.  ELEMENTS & ISOTOPES Isotopes (continued) ○ Example: all atoms of carbon have six protons, but they may have different numbers of neutrons--- carbon-14 has eight neutrons Mass number: total number of protons and neutrons in the nucleus of an atom Atomic mass: the weighted average of the masses of an element’s isotopes (“weighted” means that the amount of each isotope in nature is considered when the average mass is calculated)  ELEMENTS & ISOTOPES Radioactive isotopes: some isotopes are radioactive, which means that their nuclei are unstable and break down at a constant rate over time ○ Can be dangerous, but radioactive isotopes also have important scientific and practical uses. Geologists can determine the ages of rocks and fossils by analyzing the isotopes found in them. Radiation from certain isotopes can be used to detect cancer and to kill bacteria that causes food to spoil Radioactive isotopes can also be used as labels or “tracers” to follow the movements of substances within organisms.  ELEMENTS & ISOTOPES Radioactive isotopes (continued): ○ Example: radioactive isotope of iodine can be injected into the body and in just a few minutes, nearly all the radioactivity is found in just one place, a gland in the front of the neck called the thyroid.  CHEMICAL COMPOUNDS A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. Chemical formula: shorthand way of writing the composition of compounds ○ Example: water contains two atoms of hydrogen for each atom of oxygen and has the chemical formula H2O ○ Example: table salt contains sodium and chlorine in a 1:1 ratio, so the formula is NaCl  CHEMICAL COMPOUNDS The physical and chemical properties of a compound are usually very different from those of the elements from which it’s formed. ○ Example: hydrogen and oxygen are gases at room temperature, but they can combine explosively to form liquid water ○ Example: sodium is a silver-colored metal that is soft enough to cut with a knife and it reacts explosively with water; chlorine is a very reactive poisonous, yellow-green gas that was used as a weapon in World War I, but together as a compound, sodium chloride is table salt--- not poisonous and essential for the survival of most living things CHEMICAL COMPOUNDS  CHEMICAL BONDS Atoms in compounds are held together by chemical bonds, which involves the electrons that surround each atomic nucleus. ○ Valence electrons: electrons in an atom’s outer shell that are available to form bonds Types of chemical bonds ○ Ionic bonds: formed when one or more electrons are transferred from one atom to another Remember that atoms are electrically neutral when they have equal numbers of protons and electrons. If a neutral atom loses electrons, it becomes positively charged. If neutral atom gains electrons, it becomes more negatively charged. Positively and negatively charged atoms are called ions. CHEMICAL BONDS  CHEMICAL BONDS Types of chemical bonds (continued) ○ Covalent bonds: when atoms share electrons--- the moving electrons actually travel around the nuclei of both atoms Single covalent bond: one electron from each atom is shared Double bond: atoms share 4 electrons Triple bond: atoms share 6 electrons ○ Molecule: structure that results when atoms are joined together by covalent bonds; molecule is the smallest unit of most compounds.  CHEMICAL BONDS Weak interactions ○ In cells, many molecules interact only briefly to send signals, carry out chemical reactions, or copy info from one molecule to another. ○ Van der Waals forces: produces a slight attraction between the molecules when they are very close together. Combined Van der Waals forces along the feet of a gecko are strong enough to hold the gecko to a wall. ○ Hydrogen bonds: form between a hydrogen atom of one molecule and an oxygen or nitrogen atom of a neighboring molecule.