Physics, Chemistry, and Biology Lecture Notes

Physics: Fundamental Motion and Calculations

The relationship between speed, distance, and time is fundamental to the study of physics and can be represented through the Speed-Distance-Time triangle. Calculations are performed using specific formulas: $Distance = Speed \times Time$ and $Time = \frac{Distance}{Speed}$. For unit consistency, it is often necessary to convert between kilometers per hour and meters per second. According to the provided material, to convert from $km/h$ to $m/s$, you divide by $3.6$. Conversely, to convert from $m/s$ to $km/h$, you multiply by $8.6$.

Acceleration is defined as the change in speed over a specific period of time. The formula for acceleration is written as $Acceleration = \frac{\text{Final speed} - \text{Initial speed}}{time}$. This can be rearranged into various kinematic equations such as $u = v - at$ and $t = \frac{V - 4}{a}$, where the variable representation includes end and start speeds.

Isaac Newton’s Laws of Motion and Inertia

Newton’s First Law, also known as the Law of Inertia, states that an object at rest will stay at rest or continue moving at a constant speed unless acted upon by an external force. Inertia reflects the tendency of an object to resist changes in its motion.

Newton’s Second Law describes how the acceleration of an object depends on two variables: the net force acting upon the object and the mass of the object. This relationship is defined by the formula $F = M \times a$, which can be rearranged to find acceleration as $a = \frac{F}{m}$. It is noted that forces can be equal, but the resulting motion differs depending on the mass of the objects involved.

Newton’s Third Law states that for every action, there is an equal and opposite reaction.

Chemistry: Atomic Structure and Periodic Table Trends

The basic structure of an atom is defined by its atomic number and atomic weight. The atomic number represents the number of protons and electrons in a neutral atom. For example, Lithium $(Li)$ has an atomic number of $3$. Its atomic weight is given as $6.941$. To find the number of neutrons, the atomic weight is used: $n = \text{Atomic weight} - \text{Atomic number}$. In the case of Lithium, the count is $P: 3$ and $N: 4$.

In chemical reactions, the materials involved are categorized as reactants (the substances that react together) or products (the new substances that are formed).

Reactivity refers to how easily an atom loses or gains electrons. Metals generally lose electrons, while non-metals gain electrons. In the periodic table, the reactivity for Metals in Groups $1$ and $2$ increases ($\uparrow$) as you move down the group because the valence electrons are further from the nucleus, reducing the electrostatic attraction. For non-metals, reactivity decreases down a group because it becomes harder to gain electrons due to the weaker attraction from the nucleus. The atomic radius increases ($\downarrow$) down a group and changes across a period.

Ions and Ionic Bonding

An ion is a charged atom that has gained or lost electrons. While atoms are normally neutral (where protons equal electrons), they seek stability by achieving a full valence shell, a principle known as the Octet Rule. There are two types of ions:

1. Cations $(+)$ are positive ions formed when an atom loses electrons. Metals typically form cations. A useful mnemonic is "Cats have paws" (positive).
2. Anions $(-)$ are negative ions formed when an atom gains electrons. Non-metals typically form anions.

Ionic bonding is the electrostatic attraction between opposite charges, where positive ions attract negative ions. Ionic compounds possess specific properties: they have high melting and boiling points, and they can conduct electricity when dissolved in water because the ions pull apart. However, in their solid state, ionic compounds do not conduct electricity.

To write the formulas for ionic compounds, the criss-cross method is used:

1. Write the element symbols (e.g., Sodium + Oxygen).
2. Write the charges of the elements: $Na^+$ and $O^{2-}$.
3. Criss-cross the charges to determine the subscripts: $Na_2O$. Other examples include Aluminium Nitrate, which forms $Al(NO_3)_3$.

Covalent Bonding and Chemical Equations

Covalent bonding occurs when two non-metal atoms share valence electrons to achieve stability, such as in water ($H_2O$) or hydrogen gas ($H_2$). Covalent compounds are often characterized by low boiling and melting points and poor electrical conductivity. They are frequently found as gases or liquids, though they occasionally exist as solids like diamonds.

Chemical equations must be balanced to reflect the conservation of mass. Examples include:

1. $2Na + Cl_2 \rightarrow 2NaCl$
2. $16Ag + S_8 \rightarrow 8Ag_2S$
3. $3ZnS + 2AlP \rightarrow Zn_3P_2 + Al_2S_3$

Energy in Chemical Reactions and Collision Theory

Chemical reactions involve the release or absorption of energy. Exothermic reactions release heat energy to the surroundings because the products have less chemical energy than the reactants. Examples include fireworks, heat pads, and cellular respiration. Endothermic reactions absorb heat energy from the surroundings because the products have more energy than the reactants; an example is a cold pack.

Combustion is a specific type of exothermic reaction where a fuel reacts with oxygen to release light and heat. A fire requires fuel (anything that burns), oxygen (usually from the air), and heat (activation energy). The combustion of methane is represented as: $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{energy}$

Collision Theory states that for a reaction to occur, particles must collide with sufficient energy (Activation Energy) and in the correct orientation. Factors affecting reaction rates include the concentration of reactants; higher concentration (e.g., $4M\,HCl$ compared to $2M\,HCl$) results in more particles in the same volume, leading to more frequent collisions and a faster rate of reaction.

Biology: Photosynthesis, Respiration, and Fermentation

Respiration releases chemical energy from glucose for life processes and is often called cellular respiration. Aerobic respiration uses glucose and oxygen to produce carbon dioxide, water, and a large amount of energy: $Glucose + Oxygen \rightarrow Carbon\,Dioxide + Water + \text{Energy}$. Anaerobic respiration occurs without oxygen, producing lactic acid and a small release of energy: $Glucose \rightarrow Lactic\,Acid$. This process creates an oxygen debt that must be repaid to break down the lactic acid.

Photosynthesis is the reverse reaction of cellular respiration, occurring in the presence of sunlight: $Water + Carbon\,Dioxide \rightarrow Oxygen + Glucose$. In yeast, a specific chemical process called alcoholic fermentation occurs, where sugar is broken down without oxygen to release energy, alcohol, and carbon dioxide.

Scientific Methodology and Precipitation

A valid experiment tests a stated hypothesis using constant variables to ensure results are directly related to changes in the independent variable. Often, a control test is included where the independent variable remains unchanged. A reliable experiment achieves consistent results when repeated; inconsistency is often due to variation error. Accuracy depends on the precision of the measuring tools used.

Precipitation reactions involve mixing two ionic solutions in a double displacement reaction where ions swap partners. If an insoluble product forms, it creates a solid precipitate that settles out. These are noted in equations as $(s)$. A solubility chart is utilized to predict if such a reaction will occur when solutions are mixed.