Atoms: The Nature of Things Chapter 2

2.1 The Greek Atom: The Smallest Pieces Ancient Greeks were original thinkers who wanted to think their way to the bottom of everything. One thing they thought about was the nature of matter and what different substances had in common. Democritus focused on this question with a “thought experiment” that he imagined in principle, but was difficult to carry out in practice. He wondered how far something could be divided: forever or would there be a limit at which no further divisions were possible. The first alternative seemed absurd to him, so he concluded that matter is made of imperceptibly small “a-tomic” (meaning “not divisible”) particles that he referred to as “atoms.”

2.1 Cont. 2.1 Cont. In Democritus’ time the atomic idea had not yet been confirmed by observations, but was an educated guess or hypothesis. A scientific theory is a well-confirmed idea that explains a broad range of observations; however, no matter how often observations may be confirmed, theories can never be fact because we cannot observe every possible material object to prove for certain that everything is made of atoms. In essence, hypotheses and theories cannot be proved but they can be disproved. The Atomic Theory of Matter – All matter is made of tiny particles too small to be seen.

2.1 Cont. 2.1 Cont. Around 1800, John Dalton discovered the first specific evidence for atoms confirming that things are made of atoms. He found that when substances are combined chemically to form other substances, they combine in simple ratios by weight. The simple weight ratio is 1 to 8. For example, when hydrogen and oxygen combine to form water, one atom of oxygen and two atoms of hydrogen have a simple weight ratio of 1 to 16 because it always takes two hydrogen atoms for every one oxygen atom to form a water molecule. Dalton’s weight ratios were only the first step to confirming atoms though. A few decades later botanist Robert Brown observed with a microscope that tiny pollen grains suspended in liquid move around erratically even though the liquid itself had no observable motion.

2.1 Cont. 2.1 Cont. The idea was that atoms moved around constantly resulting from numerous atoms colliding with each pollen or dust grain every second referred to as Brownian motion. Albert Einstein did calculations based off of Brownian motion which have made it difficult to dispute the evidence of the atomic theory. His calculations helped in determining the diffusion rate.

2.2 Atoms & Molecules 2.2 Atoms & Molecules On the periodic table you will find different chemical elements listed in groups having similar properties vertically and in order of increasing atomic number. Each chemical element contains the smallest particle called an atom. The atomic number represents a particular kind of atom and as we will discuss later corresponds to the number of protons the atom contains in it nucleus. When you combine elements you create a chemical compound. A pure chemical compound that still has the characteristics of that compound when made of tiny particles that are identical and made of two or more atoms attached together is called a molecule. When a chemical compound has been broken down to the base chemical elements, chemical decomposition has occurred. Today 116 elements are known: eighty-eight occur naturally on Earth while twenty-eight are created in laboratories.

2.3 The Atom’s Explanatory Power: The Odor of Violets The atomic theory tells us that every material substance that can be picked up or touched is made of atoms. You can feel air blow on you; therefore, using the atomic theory, air is a material substance and with careful measurement air has weight showing that air is made of atoms. Brownian motion showed that a liquid moves all the time even when the liquid appeared motionless and so we can suppose that air molecules are in constant motion even in still air. Consider the odor of violets and its various molecules there must be some that make it smell. In order for a violet’s smell to spread out, odor molecules must break loose from the violet and will move around when air molecules knock the odor molecules around.

2.3 Cont. 2.3 Cont. There are two different levels that humans can see: macroscopic which is what we can see around us and the microscopic level which is phenomena at the unseen level. The microscopic level helps in understanding the states of matter which are solid state, liquid state, and gas state. Nearly every substance can exist in any one of these three states. Solids molecules are crowded against one another with precise arrangement being determined by the way the substance’s molecules push and pull on one another. Liquids molecules must not be rigidly attached to one another, but are crowded together as closely as possible. Gas molecules are widely separated and dart back and forth bouncing off a containers walls and colliding and rebounding from one another. A gas should press outward against its container and this outward press is called gas pressure.

2.3 Cont. 2.3 Cont. A complete absence of air and all other forms of matter is called a vacuum. Experiments confirm a connection between warmth and molecular motion which is true for all three states. In other words, molecules are always in random motion whether in a solid, liquid, or gas and random motion increases as the solid, liquid, or gas gets warmer. Warmth is measured quantitatively with thermometers and the resulting reading is called the temperature of the solid, liquid, or gas. Because of the macroscopic and microscopic connection of the aspects of the same phenomenon between warmth and molecular motion, scientifically it is referred to as thermal motion.

2.3 Cont. 2.3 Cont. The Microscopic Interpretation of Warmth – At the microscopic level, warmth (temperature) is the random, or disorganized, motion of a substance’s molecules. This thermal motion cannot be directly observed macroscopically but is observed instead as temperature or warmth.

2.4 Metric Distances & Powers of 10 A quantity such as the length or weight of an object is the measurement made relative to a particular standard or unit. Physics is measured more precisely in metric units. The basic metric distance unit is the meter which is approximately 39 inches long. For handling large and small numbers a technique known as the powers of 10 is used. A negative in the exponent of the power of 10’s refers to everything to the right of the decimal.

2.5 The Incredible Smallness of Atoms It’s impossible to see atoms with ordinary light because light is a wave with a wavelength that in itself is very small, but still much larger than an atom. In order to see an atom microscopically the scanning electron microscope was invented that shoots a beam of tiny material particles called electrons at the object. An electron beam is different from a light beam because electrons are made of matter and light is not. Every particle of matter has a certain kind of wave called a “matter wave” which are capable of imaging individual atoms due to the face that they have wavelengths thousands of times smaller than light wavelengths. Another microscope that can detect atoms is the scanning tunneling microscope that enables scientists to pick up individual atoms and drag them from place to place.

2.6 Atomic Materialism: Atoms and Empty Space Newtonian Physics include ideas about motion, force, and gravity. According to Democritus, in reality there are only atoms and empty space. What is meant by this is water that is hot or cold and clothing that is a certain color are just atoms that are moving in such a way as to make the brains atoms interpret the water as being hot or cold or a shirt being red. Descartes saw sense impressions as being “secondary qualities” and “primary qualities” are how the universe contains only atoms and their physical properties in addition to empty space. The philosophy that matter is the only reality and that everything is determined by its mechanical motion is the view known as materialism. One good thing about philosophy is that its arguable.

2.7 Three Atomic Models: Greek, Planetary, & Quantum The first model of the atom was the Greek Model of the Atom that depicted an unchangeable atom as a single small object. When scientists discovered a new, very lightweight, electrified particle in 1897 a new model of the atom was devised. The electrified particle came to be known as the electron which circled a very tiny central core known as the nucleus which housed neutrons and protons. This new model was called the Planetary Model of the Atom. New experiments involving electrons during the 1920’s contradicted the Planetary model and even the principles of Newtonian Physics. In order to explain the new results a new model was developed known as the Quantum Theory of the Atom.

2.8 Chemistry & Life: What Did Atoms Ever Do for You? Any rearrangement of molecules into new molecular forms is called a chemical reaction. Three chemical reactions that are important in life are burning, respiration, and photosynthesis. ◦ Burning needs a crucial component from air known as oxygen. Carbon from the burning substance combines with oxygen to from carbon dioxide. Thermal energy, although not the same thing as warmth, is related to warmth. Warmth is needed to start a substance burning. Once burning, a substance creates more than enough thermal energy to sustain itself. ◦ Respiration occurs when an animal or human absorbs carbon-based molecules from food and oxygen from air and carries them throughout the body, entering a biological cell. Respiration occurs as the cell uses these substances to create biologically useful energy. ◦ Plants generate oxygen in the same way that animals produce respiration. Sun is the needed energy of plants and the conversion of the energy to oxygen is known as photosynthesis.