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Chemistry is a fundamental science that studies the structure, properties, and changes of matter. It begins with the atom, which is the smallest unit of any element. Inside the atom are protons, neutrons, and electrons, which combine in various ways to form molecules. Chemical bonding is the force that holds atoms together and is what causes the formation of different compounds. The three main states of matter (solid, liquid, gas) are also understood under it. In addition, stoichiometry describes the proportions of substances in chemical reactions, which helps balance chemical equations. These basic concepts are key to understanding the world of chemistry. Atoms and Atomic Structure An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus (containing protons and neutrons) surrounded by electrons that orbit in energy levels. For example, A water particle is made up of oxygen and hydrogen particles. Similarly, an iron particle is made up of iron protons, neutrons, and electrons. Atomic structure refers to the arrangement of the particles within an atom. At the center of an atom is a nucleus, which contains protons and neutrons, and electrons orbit around it. For example, A hydrogen atom consists of one proton and one electron, while a helium atom has two protons, two neutrons, and two electrons. Atomic Structure of Silver: Silver is a precious and shiny metal with a simple but unique atomic structure. Silver has an atomic number of 47, which means that its nucleus contains 47 protons. It also has about 61 neutrons, which together give silver a mass number of 108. Silver's 47 electrons exist in different energy levels, the most important of which is the outermost orbital, which affects the chemical properties of silver. This unique arrangement makes silver an effective electrical and thermal insulator, making it widely used in jewelry, electrical devices, and scientific experiments. Atomic Structure of Oxygen: Oxygen is an essential non-metallic element that is present in the atmosphere as a gas and is very important for life. Its atomic number is 8, meaning that its nucleus contains 8 protons and about 8 neutrons, while it is surrounded by 8 electrons. These electrons are divided into two energy levels, of which 6 electrons are in the outer orbit. These outer electrons determine the chemical properties of oxygen and its interactions with other elements. This atomic structure of oxygen makes it an essential part of various chemical compounds such as water and carbon dioxide. Atomic Structure of Hydrogen: Hydrogen is the simplest and lightest element in the universe, and is of significant importance due to its unique atomic structure. Its atomic number is 1, meaning it has only one proton in its nucleus and usually no neutrons. Hydrogen has only one electron orbiting its first energy level. Its simple structure makes it useful in a variety of chemical properties, such as the formation of water, fuel, and organic compounds. This basic atomic structure of hydrogen also helps scientists understand and explain nuclear theories. Atomic Structure of Carbon: Carbon is an important non-metallic element that is the basis of all organic compounds. Its atomic number is 6, meaning that its nucleus contains 6 protons and usually 6 neutrons, while its 6 electrons are divided into two energy levels. The first level contains 2 electrons, and the outermost orbit contains 4 electrons, which enable carbon to form strong bonds with other elements. Its atomic structure allows it to exist in various forms, such as diamond and graphite, and this characteristic makes carbon extremely important biologically and chemically. Fundamentals of Particles Everything in the universe is made up of particles, and to understand their origin, we need to know about fundamental particles. All matter and energy are made up of the smallest particles that cannot be further divided. The most important of these are quarks, leptons (such as neutrinos), and bosons. The photon is the fundamental particle of light, while particle physics studies the properties, interactions, and motions of all these particles. Some particles also have an antiparticle, which is usually discovered in experiments or cosmic rays. All this information helps us better understand the structure of the universe, gravity, and the fundamental laws. Protons: A proton is a positively charged atomic particle that is present in the center of every atom, i.e., the nucleus. This particle indicates the atomic number of any element; that is, the number and identity of an atom will be the number of protons. The proton consists of three quarks, and its mass is a large part of the total mass of the atom. It is the basic component of atomic structure,e, and its research in particle physics has explained many scientific theories. Example: The hydrogen atom is the simplest, which has only one proton in its nucleus and no neutrons. Due to this one proton, hydrogen has an atomic number of 1. This example shows that the proton determines the identity and properties of any element. Neutrons: A neutron is a fundamental atomic particle found in the nucleus along with protons. It has no electric charge, meaning it is non-electronic. Neutrons play an important role in maintaining the stability of the atomic structure. Example: A normal atom of carbon has 6 protons and 6 neutrons, but the isotope called carbon-14 has 6 protons and 8 neutrons. It is unstable due to the excess of neutrons and emits radioactive rays, which are used in carbon dating. Electrons: An electron is a light, negatively charged atomic particle that orbits the nucleus of an atom in specific energy levels. It is a lepton and has a mass much smaller than that of a proton or neutron. Electrons play a key role in determining the chemical properties and reactions of atoms. Example: Hydrogen is the simplest atom, which has only one proton in its nucleus and only one electron around it, which orbits in the first energy level. This electron forms bonds with other elements to form compounds, such as the combination of hydrogen and oxygen in water. Atomic Number: The atomic number is the number of protons in the nucleus of an element. This number is unique for each element and determines the identity of the element and its chemical properties. Mass Number: Mass number is the total number of protons and neutrons in the nucleus of an atom. This number indicates the total atomic weight of the atom and helps in identifying isotopes. for example For example, if an atom has 6 protons and 6 neutrons, its mass number will be 12 (6 + 6 12). What are Isotopes? Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. Because of this, they have different mass numbers, but the same chemical properties. For example, there are three known isotopes of carbon: Carbon-12 (6 protons + 6 neutrons) Carbon-13 (6 protons + 7 neutrons) Carbon-14 (6 protons + 8 neutrons) Chemical Bonding and Molecular Structure A chemical bond is the force or attraction that holds two or more atoms together to form a molecule. When atoms exchange or share their electrons, they form an ionic bond or a covalent bond. Example: In water (H₂O), there is a covalent bond between hydrogen and oxygen because they share electrons. Molecular structure refers to the arrangement and spatial arrangement (structure) of atoms in which they are linked by chemical bonds. This structure determines the shape, angles, and magnetic or electrical properties of the molecule. Example: The molecular structure of water (H₂O) is bent, because the two pairs of non-bonding electrons on oxygen bend the molecule. 1. Ionic bond This bond is formed when one atom gives its electron to another atom, and an attraction arises between the two atoms due to the opposite charge. Example: In sodium chloride (salt), sodium gives an electron and chlorine receives it, thus forming an ionic bond. 2. Covalent bond: In this bond, two or more atoms share their electrons so that they can obtain a complete outer shell. Example: In water (H₂O), hydrogen and oxygen share electrons, thus forming a covalent bond. 3. Metallic bond: This bond occurs only between metal atoms, where all atoms release their electrons into a sea of electrons, which are common to all. Example: Metals like iron (Fe) and copper (Cu) have metallic bonds, which is why they are shiny, conductive, and malleable. 4. Intermolecular Forces: These are the weak forces that bind one molecule to another. These include dipole-dipole forces, van der Waals forces, and hydrogen bonds. Example: Water molecules hold together due to hydrogen bonds, which keep water in its liquid state. Electronegativity: Electronegativity is the ability of an atom to attract electrons in a chemical bond. This characteristic is different for each element, and this difference is what causes the formation of ionic or covalent bonds. Example: Fluorine has the highest electronegativity, so it attracts electrons very strongly in bonds. Lewis Structures: A Lewis structure is a structural diagram in which chemical bonds between atoms and their valence electrons are shown with the help of dots and lines. This structure helps in understanding the basic structure of the molecule. Example: The Lewis structure of water (H₂O) shows two bonds (with hydrogen) and two non-bonding electron pairs around oxygen, which shows the bent shape of the molecule. The Four States of Matter Solid: A solid is a state of matter in which the particles are in a regular and close-packed arrangement, which gives it a fixed shape and volume. In them, the molecules only vibrate, not move. Examples: Ice, Stone, Wood, Iron Liquid: A liquid is a state of matter in which the particles are held together by weak bonds and are capable of flowing. A liquid has a fixed volume but does not have a fixed shape; rather, it takes the shape of its container. Example: Water, Milk, Vinegar.Oil Gas: A gas is a state of matter in which particles are moving rapidly and have no definite shape or volume. These particles are far apart, are in constant motion, and can be easily compressed by pressure Example: Le, Oxygen, Carbon dioxide, Nitrogen, Helium. Plasma: Plasma is the fourth state of matter, formed by high temperatures or intense energy, in which gas particles become ions. In this state, the particles move freely and emit light and energy. Example: Lightning.Neon lights and plasma TVs Solutions vs Suspensions Solutions: A solution is a system in which two or more substances are mixed in such a way that they form a homogeneous mixture. The substance in the larger amount is called the solvent, while the substance dissolved in it is called the solute. A solution can contain substances in varying amounts, depending on their concentration, i.e., mass or volume, and can be in liquid, solid, or gaseous form. Examples of solutions include salt water (salt + water), sugar solution, air (a mixture of various gases), and water in alcohol, in which the substances are completely dissolved in each other. Suspensions: Mixtures are mixed systems in which two or more substances are present together but are not homogeneous, meaning that not all the components mix in the same way. They contain large particles that are suspended in the form of an insoluble substance, and after some time, settle to the bottom, which is called sedimentation. These solutions separate spontaneously over time and can be easily filtered. Mixtures are usually opaque. Everyday examples include muddy water, a mixture of sand and water, and medicinal mixtures (such as cough syrups that are shaken before use). Factors Affecting Homogeneity: Particle size of ingredients: If the particle size of the ingredients is different, uniformity can be affected, such as sand and water separating quickly. Temperature: Higher temperatures often dissolve the solution better, but some compounds can also deteriorate in heat. Agitation or stirring: If the mixture is not stirred well, the ingredients will not be evenly distributed. Solubility of ingredients in the solution: If a substance is not completely dissolved, uniformity will not be achieved. Ratio of the amounts of ingredients: If there is too much or too little of one ingredient, its balance with the rest of the ingredients may be disturbed, which affects uniformity. What is Stoichiometry Stoichiometry is the study of the quantitative ratios of components in chemical reactions (i.e., how many grams, moles, or molecules are used or produced). It tells us in what ratio the substances in a chemical equation react with each other. If we have hydrogen and oxygen gas, and we want to make water, the chemical equation would be: 2H₂ + O₂ → 2H₂O This means that 2 molecules of hydrogen and 1 molecule of oxygen combine to make 2 molecules of water. If this ratio is expressed in grams or moles, we will know how much of each element is needed. 1. Mole Concept A mole is a unit that represents 6.022 × 10²³ particles (atoms, molecules, or ions) of any substance. This is called Avogadro's number. Example: 1 mole of water (H₂O) contains 6.022 × 10²³ water molecules. If the molecular mass of water is 18 grams, then 18 grams of water 1 mole of water. 2. Balancing Chemical Equations: Balancing a chemical equation means that the number of atoms on both sides is equal, so that the Law of Conservation of Mass is satisfied. Example: Unbalanced equation: H₂ + O₂ → H₂O Balanced equation: 2H₂ + O₂ → 2H₂O Now, hydrogen and oxygen are equal on both sides. 3. Reaction Quantities: To determine how much (grams or moles) of a substance will be used or produced in a chemical reaction. Example: According to the equation above: 2 moles of hydrogen + 1 mole of oxygen → 2 moles of water If you have 4 moles of hydrogen, it will combine with 2 moles of oxygen to form 4 moles of water. Quantitative composition of compounds The quantitative composition of a compound refers to the relative amounts of elements in a chemical compound, expressed as a weight or percentage. The purpose of this is to know how much of each element is present in a compound. For example, water (H₂O) contains two hydrogen atoms and one oxygen atom, but by weight, water is about 11.1% hydrogen and 88.9% oxygen. Such information helps scientists formulate accurate formulas for compounds, predict reactions, and calculate the amounts of different substances.