Atmospheric Pressure, Gas Laws, States of Matter, and Elements
Item 3: Atmospheric Pressure and Gas Laws
Atmospheric Pressure: The pressure exerted by the atmosphere due to its weight on the surface of bodies in contact with it.
Boyle’s Law: At a constant temperature, the volume occupied by a given mass of a gas is inversely proportional to the pressure. This can be expressed as: P1 x V1 = P2 x V2.
Gay-Lussac’s First Law: If the gas pressure remains constant, the volume of a fixed mass of gas is directly proportional to the absolute temperature. The increase in volume experienced by a body with increasing temperature is called thermal dilatation.
Gay-Lussac’s Second Law: If the volume of a gas remains constant, the pressure of a fixed mass of gas is directly proportional to the absolute temperature.
Kinetic Model of Gases and States of Matter
Kinetic Model of Gases:
- Gases are formed by a large number of very small particles, especially compared to the distance that separates them.
- Between particles, there is nothing but empty space.
- These particles move continuously and in a disorderly way.
- In their motion, the particles collide with each other and against the walls of the vessel containing the gas.
- The speed of gas particles increases with increasing temperature and decreases with decreasing temperature.
Kinetic Theory of Matter:
- Solids: A solid, like salt, has a fixed volume because the particles are held together by strong forces of attraction. The particles can vibrate about their fixed positions but do not change their position.
- Liquids: Liquids, like water, have a fixed volume but can flow and adapt to any form. This is because their particles are attached, but the forces of attraction between them are weaker than in solids.
State Changes
The transition from solid to liquid is called fusion, and the inverse is solidification. The passage of liquid to gas is called vaporization, and the contrary is condensation. The passage from solid to gas is called sublimation, and the reverse is reverse sublimation. The temperature remains constant during the change of state. The temperature at which a solid melts is called the melting point, and the temperature at which a liquid boils is called the boiling point.
Metals and Nonmetals
Metals:
- Have a metallic gloss.
- Are opaque.
- Are good conductors of heat and electricity.
- Are malleable and ductile.
- With the exception of mercury, are solid at room temperature.
Nonmetals:
- Do not possess metallic sheen.
- Are bad conductors of heat and electricity.
- At room temperature, can be solid, liquid, or gas.
- In solid state, are very fragile.
- Solids have low melting and boiling points.
Mendeleev’s Periodic Classification
Mendeleev sought a criterion for the classification of the 63 elements then known, to relate similar properties. This led to the current periodic table, where the elements are ordered from left to right and top to bottom in order of increasing atomic number. The periodic table is organized into 18 groups and 7 periods.
Grouping of Atoms in Matter
Elements: Formed by the same type of atoms belonging to the same element, existing as isolated atoms or molecules.
Compounds: Made of different types of atoms belonging to different elements, mainly formed by large molecules or groupings.
Relative Molecular Mass: The relative molecular mass of an element or a compound is equal to the sum of the relative atomic masses of the atoms that appear in its formula.
Essential Elements in the Human Body
Zinc: 90% of this element is concentrated in bone and muscle tissue; the rest is located in the skin, liver, and pancreas. The daily intake of zinc can be obtained from meat, fish, and shellfish. Humans need a daily intake of 10-15 mg of zinc. It affects growth and cell reproduction.
Phosphorus: 85% of the phosphorus is bound to calcium in the bones, and the rest is used in the regulation of cell membrane balance. Phosphorus is abundant in fish, meat, and legumes. The lack of this element occurs only in people with poor diets.
Calcium: Constitutes 2% of the total weight of the human body. It is involved in muscle contraction and nerve conduction. The main sources of calcium are milk, dairy products, vegetables, and fish. Daily calcium intake should be around 1000mg.