Physical Science is a very large branch of science that deals with the study of matter and energy. It includes both Physics and Chemistry. Physics is the study of how objects in the universe move and how they use energy to interact with each other. Chemistry is the study of what objects in the universe are made of. The word chemistry comes from the Latin word “Alchemista” or alchemy. It deals with particles and how they combine to form substances.
The two most basic substances in the entire universe are matter and energy.
Matter is stuff:
takes up space: length or width = 1 dimension – meter (m); has volume (v) - size of an object 3D, measured in liters (l)
does not move by itself - needs energy to move
mass (m) - amount of matter it has; theoretically could be measured by counting the particles of an object; measured by the object’s inertia – its resistance to changing motion or how hard it is to push (Newton’s first law of motion); Mass is measured in grams or kilograms (kg)
Mass is not the same thing as weight because mass is constant and weight is not. Weight (w) is the force or pull due to gravity. Since the force of gravity may change depending on position, weight may also change. Weight is measured in Newtons (N). Newton’s second law: Force = mass times acceleration (F=MA)
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Atoms are made of electrons, protons, and neutrons. All matter is made of a combination of these particles. Normally, atoms have equal numbers of protons, neutrons, and electrons.
A charged particle is a particle of matter and a particle of energy fused together. Protons have a positive charge (+), electrons have a negative charge (-), while neutrons are neutral – no charge. Particles with the same sign attract, while those with opposite signs repel.
Every atom has a center or nucleus where the protons and neutrons are bonded together. Electrons are what make chemical reactions and are what bonds one atom to another atom to make molecules. The electrons move at specific distances around the nucleus called orbitals, energy levels, or shells. The closest or inner shell can hold a maximum of two electrons. The second shell can hold a max of 8 electrons. The third shell can hold a max of 18 electrons. The fourth shell can hold a max of 32 electrons.
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Since electrons are attracted to the nucleus, an atom's electrons will fill inner shells completely first before filling outer shells. For example, an atom with 8 protons (oxygen) will also have 8 neutrons and 8 electrons. The electrons will be placed in the following locations: 2 in the first shell and 6 in the second shell. Another example: an atom with 20 protons (calcium) will also have 20 neutrons and 20 electrons. The electrons will be placed in the following locations: 2 in the first shell, 8 in the second shell, and 10 in the outer third shell. The electrons in the outermost occupied shell determine the chemical properties of the atom and how it sticks to other atoms. It is called the valence shell.
Atoms are made of mostly empty space. If the nucleus (middle) of an atom was a car, the electron would be about the size of a basketball and would be about 20 miles away from the car. Matter feels solid despite its emptiness because the electrons are moving and the charges are repelling.
Neutrons are about the same size as protons, but are slightly larger (proton + electron). An electron is about 1 / 2000th the size of one proton.
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The only difference between one atom and another is the number of protons in its nucleus. Each atom is called an element, and is given an atomic number that relates to its number of protons. The atomic mass of an element is the number of protons plus neutrons. It is usually 2 to 2.5 times the atomic number.
Properties of an element are classed as either chemical or physical.
Examples: conductivity, reactivity, acidity, flammability
are due to the location of electrons around the atom's nucleus,
mostly the outer electrons - valence electrons
observed with a chemical reaction or chemical change - elements
are combined or separated to form a new substance
does not affect the nucleus; atomic number of each atom does
not change in a chemical reaction
compound: substance made from two or more elements
chemically bonded to form a unique substance
Examples: temperature, magnetism, volume, mass, and density are observed by examining a sample of the pure element
physical change: a substance changes its form or shape but does
not create a new substance
mixture: a combination of two or more substances that are not
chemically combined and can be readily separated without breaking atomic bonds – sand and water, alcohol and water
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Stable elements are atoms that do not readily change, react, or stick to other atoms. Atoms are stable when:
they have the same number of protons, neutrons, and electrons their outer electron shell is filled
inert: a substance does not easily undergo chemical reactions
Only the Noble Gas family of atoms (helium, neon, argon, krypton, radon, and xenon) meets both of these. These atoms do not stick to anything.
Reactive elements are atoms that try to change or combine with other elements.
An ion is a reactive atom with more or fewer electrons than protons. A positive ion or cation (+) means fewer electrons than protons. A negative ion or anion (-) means more electrons than protons.
Isotopes are reactive atoms with more or less neutrons than protons. Most isotopes are radioactive – particles spit out of the nucleus.
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Elements can also be also reactive because of their electron location. When the outer shells of atoms are not filled to max, they try to take electrons from other atoms. This is what makes atoms stick together. Rust (iron) or corrosion (all other metals) is an example of a reactive element or molecule (such as water, air, acids) whose outer electron shell is not filled. It takes electrons from other molecules breaking their bonds in order to fill its own outer shell.
The pH scale (power of hydrogen) measures the concentration of acids (hydrogen ions H+) and the concentration of bases (hydroxyl ions OH-) in a solution. A solution is where something is evenly dissolved. Acids and bases must be in a liquid form. Pure water (H2O) has a pH of 7 and is neutral. Pure water is neither an acid or a base. Acidic solutions have a low pH of 0 to >7, while basic solutions have a high pH of <7 to 14. Basic solutions are also called alkaline.
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The pH scale is a logarithm scale which means each number is 10 times greater than the next number. For example, lemon juice which has a pH of 2 is ten times more acidic than vinegar which has a pH of 3, 100 times more acidic than tomato juice which has a pH of 4, and 1000 times more acidic than black coffee which has a pH of 5.
Acids steal electrons from molecules breaking their bonds. They taste sour and are identified by a red color on blue litmus paper. Bases give electrons away breaking molecular bonds. They taste bitter, feel slippery, and are identified by the color blue on red litmus paper. Both acids and bases conduct electricity and change the color of other molecules. When mixed, they trade electrons, may neutralize if the concentrations are equal, and form salt plus water.
A buffer is a solution that resists change in pH. If you add an acid, base, or water to a buffered solution, its pH will not change much. Many life forms thrive only in a relatively small pH range so they use a buffer solution to maintain a constant pH. One example of a buffer solution found in nature is blood.
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The elements are grouped according to their chemical and physical properties. One major classification is as metals, nonmetals, and metalloids. There are more metals than any other type of element, but nonmetals make up all life as we know it.
Metals are good conductors of both electricity and heat. They are usually shiny, have high melting points, are solids at room temperature, and are malleable (able to be hammered or pressed permanently out of shape without breaking or cracking) and ductile (able to be pulled or stretched into thin wire without breaking). An alloy is a physical combination of different metals that has properties of both.
If something is a good electrical conductor, it will allow electricity/electrons to pass through it without melting or catching on fire. If something is a good electrical insulator, it will block or slow down electricity. If something is a good thermal conductor, it will allow heat to pass through it without melting or catching on fire. If something is a good thermal insulator, it will block or slow down heat.
Matter – 9Material / Thermal Conductivity (W·m−1·K−1)
Silver / 429
Stainless steel / 16
Standard glass / 1,05
Concrete / 0,9–2
Red brick / 0,69
Water / 0,58
Polyethylene (plastic) / 0,42–0,51
Wood / 0,04–0,12
Polystyrene / 0,03
Air / 0,024
Most nonmetals are gasses at room temperature. In their solid state they are usually brittle (they break rather than bend) and they are insulators of both heat and electricity. Wood and plastic are nonmetal compounds that are insulators. Carbon is a nonmetal (atomic number 6) element that is found in every living thing. A whole branch of science called Organic Chemistry studies how carbon works.
Metalloids are partly like metals and partly like nonmetals. Most are semiconductors, which means that they conduct electricity under some conditions but not others. Silicon is a very useful metalloid.
Dmitri Mendeleev, a Russian chemist, is generally given credit for developing the first periodic table in 1869. The modern Periodic Table of Elements is a chart that lines up the known elements in order of increasing atomic number and their electron locations. Element 101 is named after him.
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In the periodic table there are 7 horizontal rows called periods that align elements by their electron shells. There are 18 vertical columns called groups or families that align elements by their outer electron numbers and their similar chemical properties. Except for group 18, elements on the left side or right side of the table tend to be more reactive (they chemically bond with more elements) than elements in the middle which are more stable.
The Alkali Metal family (group 1, except for hydrogen) has elements that are very reactive and readily form compounds but are not found free in nature. They form salts and alkali (acid-neutralizing) compounds such as baking soda. In pure form, they are very soft metals which catch fire on contact with water. Some examples are lithium, sodium, and potassium.
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The Alkali Earth Metal family (group 2) has elements that are reactive and readily form compounds but are not found free in nature. In pure form, they are soft and somewhat brittle metals. Some examples are magnesium and calcium.
Transition Metals (groups 3 through 12) are typical metals. They are strong, shiny, malleable, flexible, and they conduct both heat and electricity. Some examples are titanium, copper, iron, zinc, silver, and gold.
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The Halogen family (group 17) are highly reactive nonmetals that readily form compounds, but are not found free in nature. They combine with alkali metals to form salts. Halogen means salt-former. Chlorine is a poisonous greenish-yellow gas that is used in disinfectants. When combined with sodium, a poisonous metal, table salt is formed.
The Noble Gases family (group 18 -helium, neon, argon, krypton, and xenon, and radon) has elements that are inactive, or inert. Each atom has exactly the number of electrons it needs to have a full outer shell, so these atoms almost never bond with other atoms. That is why these are all gases. Neon is used in advertising signs. Argon is used in light bulbs and welding. Helium is used in balloons and to cool things. Xenon is used in headlights for new cars. Radon is radioactive and is sometimes produced in rocks.