- A. reciprocal proportion
- B. definite proportion
- C. multiple proportion
- D. conservation of mass
(b) definite proportion
- A. neutral particles
- B. positively charged particles
- C. negatively charged particles
- D. None of the above
(c) negatively charged particles
- A. 1 : 8
- B. 8 : 1
- C. 2 : 3
- D. 1 : 3
(a) 1 : 8
- A. Atoms cannot be broken.
- B. Atoms combine in small, whole numbers to form compounds.
- C. Elements are made up of atoms.
- D. All atoms of an elements are alike
(d) All atoms of an elements are alike
- A. the atomic and the mass number are same.
- B. the mass number is same and the atomic number is different.
- C. the atomic number is same and the mass number is different
- D. both atomic and mass numbers may vary.
In all atoms of an element, the atomic number is the same, but the mass number may vary. The atomic number represents the number of protons in the nucleus of an atom, and since all atoms of a particular element have the same number of protons, they all have the same atomic number. However, the mass number, which is the sum of protons and neutrons in the nucleus, can differ between atoms of the same element. Atoms of the same element that have different numbers of neutrons are called isotopes. For example, carbon-12 and carbon-14 are both carbon atoms with the same atomic number of 6, but they have different mass numbers because they contain different numbers of neutrons. Therefore, the statement that the atomic and mass numbers are the same in all atoms of an element is incorrect. What remains constant for all atoms of an element is the atomic number, not the mass number.
Atom
same kind of
proton, electron, neutron
anion, cation
Electron
negatively
Law of Conservation of Mass – Lavoisier
Law of Constant Proportion – Joseph Proust
Cathode rays – Sir William Crookes
Anode rays – Goldstein
Neutrons – James Chadwick
The Law of Conservation of Mass states that during any chemical change, the total mass of the products is equal to the total mass of the reactants. This fundamental principle means that matter cannot be created or destroyed in a chemical reaction, only rearranged. For example, when hydrogen burns in oxygen to form water, the mass of water produced equals the combined mass of hydrogen and oxygen that reacted. This law was established by Antoine Lavoisier and forms the basis for balancing chemical equations and understanding the nature of chemical reactions.
The Law of Constant Proportions states that in a pure chemical compound, the elements are always present in definite proportions by mass, regardless of the source or method of preparation. This means that any sample of a particular compound will always contain the same elements combined in the same mass ratio. For instance, water always contains hydrogen and oxygen in the ratio of 1:8 by mass, whether it is obtained from a well, river, or laboratory synthesis. This law demonstrates that compounds have a fixed composition and helps distinguish pure substances from mixtures.
Anode rays possess several important properties that distinguish them from cathode rays. Anode rays travel in straight lines in the absence of any external field. They are composed of material particles that carry mass and energy. Anode rays are deflected by both electric and magnetic fields, demonstrating their interaction with these fields. Since they are deflected towards the negatively charged plate in an electric field, they consist of positively charged particles. These positively charged particles are actually ions or atoms that have lost electrons. The discovery of anode rays provided evidence for the existence of positive charges in atoms and contributed significantly to the understanding of atomic structure.
The valency of an element with respect to hydrogen is defined as the number of hydrogen atoms that combine with one atom of that element. For example, in methane (CH₄), carbon has a valency of 4 because four hydrogen atoms combine with one carbon atom. In ammonia (NH₃), nitrogen has a valency of 3 because three hydrogen atoms combine with one nitrogen atom. Valency is a measure of the combining capacity of an element and helps in writing chemical formulas and understanding how atoms bond with each other.
An ion or radical is formed when an atom or a group of atoms either loses or gains electrons. When an atom loses electrons, it becomes positively charged and is called a cation. When an atom gains electrons, it becomes negatively charged and is called an anion. A radical is a group of atoms that behaves as a single unit and carries a charge. For example, the hydroxide radical (OH⁻) consists of one oxygen atom and one hydrogen atom bonded together, carrying a negative charge. Ions and radicals are important in chemical reactions and the formation of ionic compounds.
A chemical equation is a shorthand representation of a chemical reaction using chemical symbols and formulas of the reactants and products. It shows which substances react together (reactants) and what new substances are formed (products). For example, the equation 2H₂ + O₂ → 2H₂O represents the reaction between hydrogen and oxygen to form water. Chemical equations must be balanced so that the number of atoms of each element is the same on both sides, obeying the Law of Conservation of Mass. They provide a concise way to communicate chemical information and are essential for understanding and predicting the outcomes of chemical reactions.
Carbon monoxide.
Nitrous oxide
Nitrogen dioxide
Phosphorous pentachloride
Na Cl = 1
C O 2 = 4
Al (PO 4 ) = 3
Ba (NO 3 ) 2 = 2
Ca Cl 2 = 2
Aluminium sulphate = Al 2 (SO 4 ) 3
Silver nitrate = AgNO 3
Magnesium oxide = MgO
Barium chloride = BaCl 2
Balanced equation:
C + O 2 → CO 2
P 4 + 10 Cl 2 → 4PCl 5
S + O 2 → SO 2
Mg + 2HCl → MgCl 2 + H 2
Skeleton equation:
C + O 2 → CO 2
P + Cl 2 → PCl 5
S + O 2 → SO 2
Mg + 2HCl → MgCl 2 + H 2
A light paddle wheel placed in the path of cathode rays begins to rotate when cathode rays fall on it because the cathode rays consist of small particles called electrons that possess both mass and energy. When these electrons strike the paddle wheel, they transfer their kinetic energy to it, causing it to rotate. This demonstrates that cathode rays are not merely waves but are composed of material particles with momentum. The impact of these energetic particles on the paddle wheel provides mechanical energy that overcomes friction and sets the wheel in motion, providing experimental evidence for the particle nature of cathode rays.
J.J. Thomson found that cathode rays were attracted by the positively charged plate and repelled by the negatively charged plate. This led him to the conclusion that the cathode rays (electrons) were made of negatively charged particles.
From this experiment, we can draw the important conclusion that water obtained from different sources such as a well, a pond, a river, and underground water always consists of the same two elements, hydrogen and oxygen, in the same ratio of 1:8 by mass. This consistency in composition regardless of the source demonstrates that water is a pure chemical compound with a fixed composition. The experiment obeys the Law of Constant Proportions, which states that in a pure chemical compound, the elements are always present in definite proportions by mass. This law was established by Joseph Proust and is fundamental to understanding the nature of chemical compounds. The fact that all water samples, regardless of their origin, maintain the same hydrogen to oxygen mass ratio confirms that the composition of a pure substance is invariant and independent of its source or method of preparation.
Monovalent ions – Li + , Cs +
Divalent ions – Ni 2+ , Cu 2+ , Ba 2+ , Zn 2+ , Cd 2+ , Hg 2+ , Pb 2+ , Mn 2+ , Fe 2+ , CO 2+ , Ca 2+ , Sr 2+
Trivalent ions – Fe 3+ , Cr 3+ , Al 3+