Click the mouse to generate a particle

Particle Simulator.py

import pygame, random, math

WHITE = (255,255,255)
BLACK = (0,0,0)
SCREENSIZE = (500,500)

pygame.init()
screen = pygame.display.set_mode(SCREENSIZE)
clock = pygame.time.Clock()

list_of_points = []

def checkPointCollisions():
    for i in range(0, len(list_of_points)):
        for j in range(i+1, len(list_of_points)):
            if list_of_points[i] == 0 or list_of_points[j] == 0:
                continue
            if abs(list_of_points[i].coordinates[0] - list_of_points[j].coordinates[0]) < list_of_points[i].size + list_of_points[j].size and abs(list_of_points[i].coordinates[1] - list_of_points[j].coordinates[1]) < list_of_points[i].size + list_of_points[j].size:
                new_coordinates = [(list_of_points[i].coordinates[0] + list_of_points[j].coordinates[0] / 2), (list_of_points[i].coordinates[1] + list_of_points[j].coordinates[1] / 2)]
                new_point = Point(new_coordinates,
                                  [(list_of_points[i].speed[0] + list_of_points[j].speed[0])/2, (list_of_points[i].speed[1] + list_of_points[j].speed[1])/2],
                                  list_of_points[i].color,
                                  list_of_points[i].size + list_of_points[j].size)
                
                list_of_points[i] = 0
                list_of_points[j] = 0
                list_of_points.append(new_point)
                
            
            

class Point(object):
    def __init__(self, coordinates, speed, color, size):
        self.coordinates = coordinates
        self.speed = speed
        self.color = color
        self.size = size

    def checkCollision(self):
        if SCREENSIZE[0] - self.coordinates[0] - self.size < 5 or self.coordinates[0] < 5:
            self.speed[0] = self.speed[0] * -1
        if SCREENSIZE[1] - self.coordinates[1] - self.size < 5 or self.coordinates[1] < 5:
            self.speed[1] = self.speed[1] * -1
        
def createPoint(n):
    for i in range(n):
        random_coordinates = [random.randint(0,SCREENSIZE[0]),
                              random.randint(0,SCREENSIZE[1])]
        random_speed = [random.randint(-5,5), random.randint(-5,5)]
        if random_speed[0] == 0:
            random_speed[0] += 1
        elif random_speed[1] == 0:
            random_speed[1] += 1
        random_color = (random.randint(0,255),
                        random.randint(0,255),
                        random.randint(0,255))
        random_size = random.randint(3, 10)
        list_of_points.append(Point(random_coordinates, random_speed, random_color, random_size))

while True:
    screen.fill(BLACK)

    for event in pygame.event.get():
        if event.type == pygame.MOUSEBUTTONDOWN:
            createPoint(1)

    checkPointCollisions()
    for point in list_of_points:
        if point == 0:
            continue
        else:
            point.checkCollision()
            point.coordinates[0] += point.speed[0]
            point.coordinates[1] += point.speed[1]

    for point in list_of_points:
        if point != 0:
           pygame.draw.rect(screen,
                         point.color,
                         (point.coordinates[0], point.coordinates[1],
                          point.size, point.size))

    pygame.display.update()
    clock.tick(60)