CAP 1 - Scientists and Specta Flashcards
(21 cards)
Explain that electrons exist in distinct energy levels
Electrons exist in distinct energy levels or shells around the nucleus of an atom, with each level having a specific amount of energy. The Bohr model proposed that electrons can only occupy certain quantized energy levels and do not radiate energy while in these stable orbits. Electrons can absorb or emit energy when they jump between these levels, and the energy corresponds to the difference between the levels. Electrons fill the lowest energy levels first, and their arrangement in these levels explains phenomena like atomic spectra. These energy levels help define the structure and behavior of atoms.
Explain that atomic orbitals have different energy levels and occupy different regions of space
Atomic orbitals are regions of space where electrons are most likely found, and they exist at different energy levels. Each energy level (n = 1, 2, 3…) contains sublevels (s, p, d, f) with distinct shapes and energies. Lower-energy orbitals (s, p) are closer to the nucleus, while higher-energy orbitals (d, f) extend farther. Electrons move within these orbitals, not in fixed paths, following quantum mechanics. This model explains the structure and behaviour of atoms more accurately than earlier models.
Explain how the transition of electrons between energy levels can produce absorption and emission line spectra
Electrons in atoms exist in quantized energy levels, meaning they can only occupy specific energy states. When electrons move between these levels, they absorb or emit energy in the form of light (photons). This process creates atomic absorption and emission spectra, which are unique to each element.
Atomic Absorption occurs when an atom absorbs energy (e.g. from heat or light), and an electron jumps from a lower energy level to a higher one (excited state). The energy absorbed must match the exact energy difference between the 2 levels. The absorbed energy corresponds to specific wavelengths od light, which appear as dark lines in an otherwise continuous spectrum. This is called an absorption spectrum and is used to identify elements in stars and gases.
Atomic emission occurs when an excited electron returns to a lower energy level, where it releases energy in the form of a photon. The emitted light has specific wavelengths corresponding to the energy difference between levels. These emitted wavelengths appear as bright lines in a dark background, forming an emission spectrum.
Describe what the flame test is and how the flame test can be used to identify elements
A sample containing metal ions is placed on a flame using a nichrome wire loop. The heat from the Bunsen burner excites the electrons in the metal atoms, causing them to move to higher energy levels. When the electrons return to their ground state, they emit light at specific wavelengths, producing a characteristic flame colour unique to each element.
Describe the advantages and limitations of the flame test
Advantages: Quick and simple way to identify metal ions, used in fireworks, helpful in qualitative analysis of unknown substances
Limitations: Not highly precise (similar colours may overlap), can only detect elements with bright, visible emissions, low concentrations of elements may not be detected, contamination may occur, not quantitative data.
Describe what atomic absorption spectroscopy is and how it can be used to identify elements
Sample of substance is vapourised (atomised), creating a vapour of free metal atoms. Light of specific frequencies shone through it (from a hollow cathode lamp of same element being tested for). The atoms absorb some of these light/photons as electrons jump to higher energy levels, with remaining light having frequencies missing. The specific frequencies missing identify the element. Intensity of absorptions gives the concentration of metal in the sample.
Describe the advantages and uses of atomic absorption spectroscopy
Advantages: Can detect very low concentrations of elements, works for multiple elements in a single sample, used for quantitative analysis as well, used in fields like environmental testing, medical diagnostics, medial science
Uses: Detecting toxic metals, analysing blood samples, checking soil samples for metal content
Describe the role of John Dalton in the development of the atomic model as well as any relevant experiments
In 1803 proposed that all matter comprises of tiny, indivisible particles called atoms, each with unique properties that could not be created, destroyed, or divided. He proposed that elements have unique properties and that atoms combine in fixed, whole-number ratios to form compounds. He stated that atoms are rearranged in chemical reactions but do not change identity. His atomic model was solid, indivisible spheres. He discovered this by experiments with gases where he observed that elements combine in simple ratios.
Describe the role of JJ Thomson in the development of the atomic model as well as any relevant experiments
In 1897 discovered the electron through his experiments with cathode rays. He proposed the plum pudding model of the atom where electrons were embedded in a positively charge sphere.
J.J. Thomson’s Cathode Ray Experiment led to the discovery of the electron, proving that atoms were not indivisible. He used a cathode ray tube, where he observed that a mysterious ray travelled from the negative electrode (cathode) to the positive electrode (anode). By applying electric and magnetic fields, he found that the ray was negatively charged and deflected predictably, indicating it was made of tiny particles. He also determined that these particles had the same charge-to-mass ratio regardless of the gas inside the tube, suggesting they were a fundamental part of all atoms. This led him to propose the Plum Pudding Model, where electrons were embedded in a diffuse positive charge, like “raisins in a pudding.”
Describe the role of Ernest Rutherford in the development of the atomic model as well as any relevant experiments
In 1911 he described an atom as having a tiny, dense, positively charged core called a nucleus that contains most of the atom’s mass. The light, negatively charged, electrons circulated this nucleus, much like planets revolving around the sun. This led to him proposing the Rutherford Atomic Model
Gold Foil Experiment: Fired alpha particles (positively charged) at a thin sheet of gold foil and a fluorescent screen surrounded the foil to detect the deflected particles. Most alpha particles passed straight through the foil, indicating atoms are mostly empty space while a few bounced backs (some directly), indicating a dense, positively charged core. This disproved the plum pudding model and led to the Nuclear Model of the Atom (or the Rutherford Atomic Model).
Describe the role of Niels Bohr in the development of the atomic model as well as any relevant experiments
In 1913 proposed a model of the atom in which the electron could only occupy certain orbits around the nucleus. Electrons orbited the nucleus in fixed, quantized energy levels/shells, each with a specific energy. The atomic model was the first to use quantum theory, in that the electrons were limited to specific orbits around the nucleus.
Bohr’s experiment: Used the observed spectral lines of hydrogen to support his model. Hydrogen, when energized emits light at specific wavelengths. Bohr explained this means that the electron in a hydrogen atom could only occupy discrete energy levels.
Describe the role of James Chadwick in the development of the atomic model as well as any relevant experiments
In 1932, James Chadwick discovered the neutron and was able to measure a neutrons mass based on their interaction with protons.
Chadwick experiment: Chadwick bombarded beryllium with alpha particles, and it emitted a type of radiation that was not deflected by electric or magnetic fields (as charged particles would be). Radiation seemed to consist of particles with no electric charge and a mass like protons. Concluded these particles were neutrons – had no charge, mass roughly equal to protons, prevented electrostatic repulsion between protons.
Explain how developments in technology have contributed to our understanding of the model of the atom
Dalton – used basic experimental apparatus
Thomson – used cathode ray tubes (CRT)
Rutherford – used gold foil experiment setup with alpha particle sources and detectors (fluorescent screens)
Bohr – used advanced spectrometers to study the spectral lines of hydrogen
Chadwick – used particle accelerators and alpha particle bombardment of beryllium
Describe the structure of the atom, including the locations of sub-atomic particles, holding the electrons to the nucleus
The atom has a positively charged nucleus consisting of protons and neutrons in the centre of the atom. Electrons surround the neutrons in different energy levels/clouds. Electrostatic attraction between positively charged protons and negatively charged electrons keeps electrons bound to the nucleus
Describe differences in properties of isotopes of the same element
Isotopes of an element have identical chemical properties because they have the same electron configuration, but they may have different physical properties, such as mass and stability. Some isotopes are radioactive, meaning they decay over time, while others are stable.
Define what the relative atomic mass of an element is, and explain how this is different from mass numbe
Relative Atomic Mass (Ar) is the weighted average mass of an atom of an element compared to 1/12th of the mass of a carbon-12 atom. It considers the different isotopes of an element and their relative abundances. Since it is an average, it is usually not a whole number. Mass Number (A) is the total number of protons and neutrons in the nucleus of a specific atom. It is always a whole number and represents a single isotope of an element
Simply explain JJ Thomson’s cathode ray experiment and how it led to his discovery of the electron
JJ Thomson’s cathode ray experiment (1897) demonstrated the existence of electrons, proving that atoms are divisible. He used a vacuum tube with electrodes and observed a beam (cathode rays) traveling from the cathode to the anode. When exposed to electric and magnetic fields, the beam was deflected toward the positively charged plate, indicating it was made of negatively charged particles. By calculating the charge-to-mass ratio, Thomson concluded these particles were much smaller than atoms. This led to his “plum pudding model”, where electrons were embedded in a positively charged “soup.”
Explain why the emission spectra of different elements are not the same, and how this affects observations from a flame test
The emission spectra of different elements are unique because each element has a distinct atomic structure, leading to specific electron energy levels. When an atom absorbs energy (e.g., from heat in a flame), its electrons move to higher energy levels. When they return to lower energy levels, they emit light at characteristic wavelengths corresponding to the energy differences between these levels. These wavelengths form an element’s unique emission spectrum.
In a flame test, these differences in emission spectra cause different elements to produce different flame colours. Since no two elements have the same set of energy levels, their emission spectra (and thus flame colors) are unique, allowing for identification of elements based on their characteristic flame colors.
List different physical properties of an element
Melting Point
Boiling Point
Density
Color
State of Matter
Electrical Conductivity
Thermal Conductivity
Malleability
Ductility
Luster
Hardness
Solubility
Magnetism
Describe using a step-by-step method how you could use a flame test to identify which salt is contained in a sample.
Prepare the Wire Loop:
Clean the nichrome or platinum wire loop by dipping it into hydrochloric acid (HCl) and then holding it in the hottest part of the Bunsen burner flame until no color is seen in the flame.
Repeat if necessary to ensure the wire is free of contaminants.
Obtain the Salt Sample:
Moisten the cleaned wire loop by dipping it into distilled water.
Dip the wet wire into the unknown salt sample so that a small amount sticks to the loop.
Perform the Flame Test:
Place the salt-coated wire loop into the hottest part of the Bunsen burner flame (usually the blue inner cone).
Observe the color of the flame carefully.
Compare with Known Flame Colors:
Compare the observed flame color with reference flame colors of known metal salts:
Sodium (Na) → Bright yellow
Potassium (K) → Lilac (pale purple)
Calcium (Ca) → Orange-red
Strontium (Sr) → Bright red
Copper (Cu) → Blue-green
Barium (Ba) → Yellow-green
Confirm the Identity:
If the observed color is unclear or influenced by contamination (e.g., sodium’s yellow is intense and may overpower others), repeat the test with a fresh sample and a well-cleaned wire.
If necessary, use a cobalt blue glass filter to block sodium’s yellow color and help see other flame colors more clearly (e.g., potassium’s lilac).
Record and Conclude:
Based on the observed flame color, determine which metal ion is present in the unknown salt.
If multiple colors appear, consider the possibility of a mixture of salts.
List different chemical properties in an element
Reactivity
Flammability
Oxidation State
Corrosion Resistance
Acid-Base Behavior
Electronegativity
Ionization Energy
Toxicity
Radioactivity
Combustibility
