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Answer:
The identity of an element is determined by its atomic number, which equals the number of protons in the nucleus. Every atom of a given element has the same number of protons; this number cannot change without transforming the atom into a different element. For example, hydrogen has 1 proton (atomic number 1), so any atom with 1 proton is hydrogen. Carbon has 6 protons (atomic number 6), and oxygen has 8 protons (atomic number 8). If an atom gains or loses protons, it becomes a different element. Electrons and neutrons may vary (forming ions or isotopes), but the proton count is the defining feature.
Answer:
An atom is made of three main sub-atomic particles: protons, neutrons, and electrons. Protons are positively charged (+1) and are located in the nucleus; they have a relative mass of about 1 atomic mass unit (amu). Neutrons have no charge (0), are also in the nucleus, and have a mass nearly equal to a proton (about 1 amu). Electrons are negatively charged (−1), have a very small mass (about 1/1836 of a proton), and move around the nucleus in the electron cloud or shells. Together, protons and neutrons form most of the atom’s mass, while electrons occupy most of the atom’s volume.
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Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Because they have the same proton count, isotopes share chemical properties and the same atomic number, but they differ in mass number and physical properties. For example, carbon has isotopes ¹²C (6 protons, 6 neutrons) and ¹⁴C (6 protons, 8 neutrons). Both are chemically carbon and react similarly in chemical reactions, but ¹⁴C is radioactive while ¹²C is stable; their masses differ. Thus isotopes are useful in dating (like ¹⁴C in archaeology) and in medicine (radioisotopes).
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An atom is normally electrically neutral because it contains an equal number of protons (+) and electrons (−), so the total positive and negative charges balance. When an atom gains electrons, it acquires extra negative charge and becomes a negative ion (anion); for example, a chlorine atom gains one electron to become Cl⁻ in sodium chloride formation. When an atom loses electrons, it has more positive charge and becomes a positive ion (cation); for example, a sodium atom loses one electron to form Na⁺ in the same salt. These ion changes are central to bonding and electrical conductivity in solutions.
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Sulfur and phosphorus are different elements because they have different atomic numbers. Phosphorus (P) has 15 protons (atomic number 15), while sulfur (S) has 16 protons (atomic number 16). This one-proton difference changes their electron arrangements and thus chemical behavior. Phosphorus typically forms compounds like PCl₃ or P₄ in different allotropes and commonly exhibits oxidation states such as +3 and +5. Sulfur forms S₈ rings and commonly shows oxidation states like −2, +4, and +6, making it more versatile in forming oxoacids like H₂SO₄. Although both are non-metals and near each other in the periodic table, the extra proton (and associated electron) in sulfur makes it slightly more electronegative and changes bonding tendencies.
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J.J. Thomson discovered the electron using cathode ray experiments, showing atoms contain small negatively charged particles. This led to the plum pudding model, where electrons were thought to be embedded in a positive 'pudding.' Rutherford’s gold foil experiment then showed most alpha particles passed through the foil, but some were deflected strongly. This demonstrated that positive charge and most mass are concentrated in a small dense nucleus, not spread out. Rutherford’s result replaced the plum pudding with a nuclear model: electrons orbit a compact nucleus containing protons (and later neutrons). Together, these discoveries showed the atom is divisible, has internal structure, and moved science from a solid indivisible particle concept to a complex model with distinct regions for mass (nucleus) and volume (electron cloud).
Answer:
Removing an electron from a neutral hydrogen atom (which has one proton and one electron) leaves a single proton with a positive charge. The resulting species is the hydrogen ion or proton, symbolized as H⁺. Charge: it becomes positively charged because the negative electron is gone. Structure: there is no electron cloud left around the nucleus, so the particle is just a bare proton. Chemically, H⁺ is the simplest cation and plays a central role in acid–base chemistry; in water it exists as hydronium ion (H₃O⁺) rather than a free proton. Naturally, H⁺ (as H₃O⁺) exists in acidic solutions, such as stomach acid and rainwater with dissolved CO₂ (forming weak acids).
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¹⁶O, ¹⁷O, and ¹⁸O are isotopes of oxygen; all have 8 protons, so chemically they behave similarly and form the same kinds of bonds (e.g., in H₂O, CO₂). Their chemical reactions depend mainly on electron configuration, unchanged by neutron number. However, differing neutron counts change their masses, affecting physical properties like diffusion rates, vapor pressures, and reaction kinetics slightly. Scientists exploit these differences: ¹⁸O/¹⁶O ratios in ice cores and marine carbonates help reconstruct past climate and temperatures (paleoclimatology). ¹⁷O and ¹⁸O are used as tracers in biochemistry and geochemistry to follow pathways of water and oxygen. Thus isotopes are invaluable tools because identical chemistry but different mass produce measurable physical effects.
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According to atomic theory and the law of conservation of mass, atoms are neither created nor destroyed in a chemical reaction; they are simply rearranged to form new substances. This means the number and type of each atom remain the same before and after reaction. For example, combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O (showing subscripts as CH₄, O₂, CO₂, H₂O). Count atoms: C:1 → 1, H:4 → 2×2 = 4, O:4 → 2 (in CO₂) + 2×1 (in 2H₂O) = 4. Every atom present in reactants appears in products, only bonds are broken and new bonds formed. This explains why mass is conserved and why balanced chemical equations are essential.
Answer:
When equal numbers of sodium (Na) and chlorine (Cl) atoms react, electron transfer occurs: each Na atom loses one electron to become Na⁺, and each Cl atom gains one electron to become Cl⁻. This electron transfer creates oppositely charged ions that attract each other by electrostatic forces, forming an ionic bond. The resulting compound sodium chloride (NaCl) is made of a regular three-dimensional crystal lattice where each Na⁺ is surrounded by Cl⁻ ions and each Cl⁻ by Na⁺ ions. The overall compound is electrically neutral because the positive and negative charges balance. This ionic structure explains NaCl’s high melting point and its ability to conduct electricity when molten or dissolved in water.