SNC1 Chemistry — Density, Atomic Structure, and Physical Properties Review Flashcards

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Density

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Density is the mass of a substance per unit volume and is calculated using the formula $\text{density} = \frac{\text{mass}}{\text{volume}}$. It is expressed in units such as $\text{g/mL}$, $\text{g/cm}^3$, or $\text{kg/m}^3$ and helps predict whether substances will float or sink in a fluid.

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Mass number

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The mass number is the total number of protons and neutrons in an atom's nucleus. It is used to distinguish isotopes and is usually an integer close to the atomic mass on the periodic table.

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Atomic number

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The atomic number is the number of protons in an atom and determines the element's identity. In a neutral atom, the atomic number also equals the number of electrons.

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Isotope

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Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, giving them different mass numbers. Isotopes have nearly identical chemical properties but can differ in nuclear stability.

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Proton

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A proton is a positively charged subatomic particle found in the nucleus of an atom, and its number defines the element (the atomic number). Protons contribute to nearly all of an atom's mass along with neutrons.

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Neutron

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A neutron is an uncharged subatomic particle located in the nucleus; it contributes to atomic mass and affects isotopic identity. Neutron count equals mass number minus atomic number.

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Electron

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An electron is a negatively charged subatomic particle that orbits the nucleus in energy levels or shells. In a neutral atom, the number of electrons equals the number of protons.

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Bohr model

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The Bohr model represents electrons in discrete energy levels (shells) around a central nucleus and is useful for visualizing electron arrangement for elements up to about atomic number 20. It shows how electrons fill shells in patterns like $2,8,8$ for many elements.

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Energy level

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An energy level (or electron shell) is a region around the nucleus where electrons of similar energy are likely to be found. Higher energy levels can hold more electrons and are filled according to specific patterns.

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Physical property

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A physical property is a characteristic of a substance that can be observed or measured without changing its chemical identity, such as color, density, melting point, or conductivity. Physical properties can be qualitative or quantitative.

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Chemical property

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A chemical property describes how a substance interacts with other substances and changes composition during chemical reactions. Examples include flammability, reactivity with acid, and oxidation behavior.

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Malleability vs Ductility

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Malleability is the ability of a solid to be pounded or rolled into thin sheets, while ductility is the ability to be drawn into a wire. Both are mechanical physical properties related to how metals deform under stress.

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Adhesion and Cohesion

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Adhesion is the attraction between different substances (e.g., water and glass), while cohesion is the attraction between like molecules (e.g., water molecules to each other). These forces explain phenomena like meniscus formation and why some liquids wet surfaces.

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Meniscus

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A meniscus is the curve seen at a liquid's surface in a container, resulting from adhesive forces between the liquid and container walls and cohesive forces within the liquid. Measurements of volume in a graduated cylinder should be read at the bottom of the meniscus.

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Solubility

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Solubility quantifies how much of a substance can dissolve in a solvent at a given temperature, often expressed as mg per 100 mL of water. Comparing solubility values indicates which compound is more soluble under the same conditions.

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Volume displacement

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Volume displacement measures an object's volume by the change in fluid level when the object is submerged; the displaced volume equals the object's volume. This method is commonly used to find volume for irregular solids.

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Units conversion for density

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Density units must match mass and volume units used; for example, $1\,\text{g/mL} = 1000\,\text{kg/m}^3$. Proper conversion is essential when solving density problems across different unit systems.

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Buoyancy and ship floatation

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An object floats when its average density is less than the fluid's density; large ships float despite dense materials because hollow spaces reduce overall average density. Design geometry and trapped air are key to lowering average density.

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Counting subatomic particles

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To find protons, neutrons, and electrons: protons = atomic number, electrons = protons for neutral atoms, and neutrons = mass number minus atomic number. This method identifies isotopes and electronic configurations.

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Notation of isotopes

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Isotope notation uses the element name or symbol with the mass number, such as hydrogen-2 for the isotope with mass number $2$. The naming shows how many total nucleons are present in that isotope.