Atoms Molecules and Crystals Flashcards
(11 cards)
Structure of an Atom
The different types of models of atoms:
1. Dalton’s Billiard Ball Model: Dalton’s atomic model, proposed in the early 19th century, suggested that atoms are tiny, indivisible particles, like billiard balls. He proposed that each element consisted of unique atoms, with different elements having atoms of varying masses. According to Dalton, atoms combine in simple whole-number ratios to form compounds.
2. Thomson’s Plum Pudding Model: depicted the atom as a positively charged sphere with embedded electrons. He compared it to a plum pudding, where electrons were like negatively charged plums embedded in a positively charged pudding. This model suggested that atoms were not indivisible but consisted of smaller, negatively charged particles (electrons) within a positively charged matrix.
3. Rutherford’s Model: introduced the concept of a nuclear atom. He suggested that atoms have a dense, positively charged nucleus at their center, surrounded by orbiting electrons. Rutherford’s famous gold foil experiment demonstrated that most of an atom’s mass and positive charge is concentrated in the nucleus, while electrons occupy the vast empty space around it.
4. Bohr’s Model: introduced quantized electron energy levels. He suggested that electrons orbit the nucleus in specific, fixed orbits or energy levels. Electrons can only occupy these allowed orbits, and they emit or absorb energy when transitioning between them
Mendeleev’s Periodic Table
Dmitri Mendeleev’s periodic table is a tabular arrangement of chemical elements organized by increasing atomic number and similar chemical properties. Elements are grouped into rows (periods) and columns (groups) based on their valence electrons. Mendeleev’s table helped predict the existence and properties of undiscovered elements, leaving gaps for them. This led to the discovery of new elements and confirmed the periodicity of chemical properties. It became the most popular cause it was the easiest to print.
Why Periodicity?
The periodicity of an atom depends on the number of electrons in the last orbital (aka the valence electrons).
Certain atoms get more stable on losing a few electrons while others need some extra ones to be more stable
Atomic Bonding
When two atoms come together, their valence orbital overlap and
valence electrons get shared (covalent bonding)
or valence electrons leaves and goes to another (ionic bonding)
(the minimum required energy for each type of bond determines the type of bond that will eventually occur).
Typically, covalent bond results when the outer orbitals of the atoms have half of the total number of electrons needed to saturate the orbital.
Typically, ionic bond results when the outer orbital of one atom has one or two electrons missing to saturate the orbital, and the other has only one or two electrons in the last orbital.
What is Matter?
Matter is anything with mass and volume, composed of atoms. It exists in different states (solid, liquid, gas, or plasma) and undergoes physical and chemical changes. Governed by the law of conservation of mass, matter is the fundamental substance of the universe, ranging from subatomic particles to celestial bodies. They are cluster of atoms or molecules which may or may not be bonded.
Intermolecular Forces and States of Matter
Intermolecular Force (aka Van der Waal forces) are the forces of attraction between particles in condensed matter as a result of electrostatic attraction and this force is very weak in strength. However when a large number of molecules are put together, the collective force is a lot more.
In solids, the matter is tightly packed and no space between atoms
In liquids, there are more gaps between atoms
In gases, there are mostly gaps and atoms littered in between
Gecko adhesive system is a good example of Van der Waal forces. Geckos can stick to walls because of tiny hairs on their feet. These hairs create a lot of tiny forces that help them stay put. These forces, called van der Waals forces, happen when molecules get close together. It’s like when magnets stick together but much weaker. The gecko’s special hairs and these weak forces allow them to walk on walls and ceilings.
Properties of Solids
- Definite Shape and Volume
- Strong Intermolecular Forces
short range order- amorphous, long range order- crystalline
Atomic Arrangement
Crystalline- Crystalline solids have an ordered, repeating arrangement of atoms or molecules in a three-dimensional lattice structure. ex: Quartz
Amorphous- Amorphous solids lack long-range order and have a random or disordered atomic arrangement. ex: Glass
Both Quartz and Glass are SiO2 but due to their differing atomic arrangement, their properties also differ.
X-Ray Diffraction to determine atomic structure
Types of Crystalline
Properties of Crystalline Solids
